Add instructions to build the Flatpak package locally

README.md

@@ -80,6 +80,20 @@ Diffuse.  The `XDG_CONFIG_HOME` and `XDG_DATA_DIR` environment variables
 indicate where Diffuse should store persistent settings (eg. the path to a
 writable directory on the pen drive).
 
+## Building and testing the Flatpak package
+
+To install Diffuse locally:
+
+    flatpak-builder builddir-flatpak --user --install com.github.mightycreak.Diffuse.yml
+
+To run Diffuse through Flatpak:
+
+    flatpak run com.github.mightycreak.Diffuse
+
+To uninstall Diffuse:
+
+    flatpak remove com.github.mightycreak.Diffuse
+
 ## Help Documentation
 
 Diffuse's help documentation is written in the DocBook format and can be easily