Create How to Install.md

Linux, BSD, macOS

How to Install.md

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+# How to install PhotoGIMP
+
+## On Linux with flatpak version of GIMP
+
+Extract all hidden folders
+
+- `.icons`
+- `.var`
+- `.local`
+
+to your Home directory and you are done.
+
+## On Linux with GIMP installed through package manager —or— On *BSD
+
+Extract all hidden folders
+
+- `.icons`
+- `.var`
+- `.local`
+
+to your Home directory and then move the subfolder 
+
+- `.var/app/org.gimp.GIMP/config/GIMP/2.10`  
+
+to `~/.config/gimp/2.10`.
+
+Afterwards you can delete `.var/app/org.gimp.GIMP` respectively `.var` (if not used otherwise!).
+
+## On macOS
+
+Unpack the whole archive and copy/move only the subfolder  
+—or—  
+Extract only the subfolder
+
+- `.var/app/org.gimp.GIMP/config/GIMP/2.10`  
+(inside the hidden folder `.var`)
+
+into the folder `~/Library/Application Support/GIMP`.
+
+Afterwards you can delete `.var`.