Added CONTRIBUTING.md (#169)

CONTRIBUTING.md

@@ -0,0 +1,128 @@
+# Contributing
+
+Thanks for helping with SlimeVR! This document explains what to know when
+contributing.
+
+We are most active on [Discord](https://discord.gg/SlimeVR), come chat with us if you
+have any questions or want to hang out! 😎
+
+## Setting up the development environment
+
+We use PlatformIO as our build tooling and rely on Git for version control. There are
+instructions to set all of this up [here](https://docs.slimevr.dev/firmware/setup-and-install.html).
+
+## Using third-party code
+
+Often you will want to use or reference third-party code. You should not just
+copy-paste code from random libraries! There are several reasons for this:
+
+- It is not clear when/where the code originated from.
+- The original code's license needs to be kept intact.
+- It removes the ability to update our code when the original updates.
+- It makes it harder for us to maintain the code, because we don't know what has changed
+  from the original!
+
+Instead, we will want to do the following:
+1. Check that the dependency has a permissive license.
+1. (Optional) Fork the dependency if it needs any modification.
+1. Add the dependency via PlatformIO.
+
+### Check the license
+
+The SlimeVR firmware is under the MIT License and also is intended to be permissively
+licensed. This means that we will not accept contributions that include code from any
+viral software licenses. If you do not know what that means, here is a breakdown of some
+common software licenses:
+
+> Fine to use:
+> * MIT
+> * Apache 2.0
+> * BSD
+>
+> Will not be accepted:
+> * GPLv3 or v2
+> * LGPL
+> * No license
+
+This includes the license of any code that your dependency depends on! If you are ever
+unsure, feel free to ask us in our Discord.
+
+### (Optional) Fork the dependency
+
+When you want to use the depdendency, you should ask yourself: "Can I simply call the
+functions/classes in the dependency from *my* code, or do I actually need to modify the
+source code of the original files"? If the answer is "I need to modify the original
+files", then you will need to fork the dependency so that your modifications are clear.
+
+> **Note**
+> If you have never forked on GitHub before, a fork is basically a copy of a library that
+> maintains the original's history. This means that any changes you commit in your fork
+> will show up as changes against the original. We can even update these changes as the
+> original changes!
+
+To create a fork in GitHub, simply go to the original library and click this button:
+![](https://docs.github.com/assets/cb-28613/images/help/repository/fork_button.png)
+Now clone your repo to your computer. From this point forward, any changes that you
+make while working on your fork will have their Git history preserved and linked to the
+original when you commit those changes.
+
+We will likely ask you to transfer ownership of the fork to the SlimeVR organization if
+your PR is going to be merged.
+
+
+### Adding the dependency
+
+PlatformIO provides us a helpful way to do dependency management. 
+Here we provide the basic workflow you can follow, but you can refer to the 
+[PlatformIO documentation on dependecies][dep docs] for more details.
+
+[dep docs]: https://docs.platformio.org/en/latest/librarymanager/dependencies.html
+
+PlatformIO gives us a helpful way to do dependency management, which you can read an
+overview of [here](https://docs.platformio.org/en/latest/librarymanager/dependencies.html).
+But to save you time, we have outlined the basic workflow for you.
+
+There is a field called `lib_deps` in the `platformio.ini` file that describes the list
+of dependencies in the code. These are third-party libraries located outside the main
+firmware git repo. You want to add your dependency to this list. The full list of
+options for this field is outlined [here], but for simplicity, there are a few common
+ways of giving dependencies:
+
+[here]: https://docs.platformio.org/en/latest/core/userguide/pkg/cmd_install.html#cmd-pkg-install-specifications
+
+```ini
+[env]
+lib_deps=
+  bblanchon/ArduinoJson@6.9.12
+  https://github.com/Some/Dependency.git#v1.2.3
+  symlink://C:/path/to/the/library
+```
+
+In order, these dependencies do the following:
+1. Adds a dependency on version `6.9.12` of the
+  [ArduinoJson](https://registry.platformio.org/libraries/bblanchon/ArduinoJson)
+  library by `bblanchon`. This library was uploaded to the PlatformIO
+  [package registry](https://registry.platformio.org/search) which contains many popular
+  libraries intended for use with PlatformIO.
+1. Adds a dependency to a Git repo located at `https://github.com/Some/Dependency` and
+  uses the commit tagged as `v1.2.3`. This could also have been a branch name, or a
+  commit hash.
+1. Links to a folder locally on your computer with the path `C:/path/to/the/library`.
+  This is useful when testing your code locally where you want to make changes in your
+  fork (which is checked out at that path), but you don't want to have to constantly
+  commit and push to your fork just to get the changes usable by the firmware.
+
+> **Note**
+> If you have forked the dependency instead of using it as-is, we recommend using the
+> `symlink://` approach while developing locally, and then using the Git approach when
+> submitting your code for a pull request. This is because while developing locally,
+> you will want to test out frequent changes and won't want to have to push constantly
+> to Git and have PlatformIO constantly retrieve those changes. However, for anyone
+> else to be able to use your code, it needs to be in a Git repository rather than a symlink.
+>
+> Once you are done doing local testing and are ready to submit a PR, you can push
+> whatever changes you made to the forked dependency to its repository, and switch the
+> firmware's `lib_deps` back to the Git url.
+>
+> Dont forget that your fork will need to be pushed and publicly viewable on GitHub for
+> us to be able to use and review it!