flatpak-run: add page (#13518)

Co-authored-by: spageektti <git@spageektti.cc>

pages/linux/flatpak-run.md

@@ -0,0 +1,16 @@
+# flatpak run
+
+> Run flatpak applications and runtimes.
+> More information: <https://docs.flatpak.org/en/latest/flatpak-command-reference.html#flatpak-run>.
+
+- Run an installed application:
+
+`flatpak run {{com.example.app}}`
+
+- Run an installed application from a specific branch e.g. stable, beta, master:
+
+`flatpak run --branch={{stable|beta|master|...}} {{com.example.app}}`
+
+- Run an interactive shell inside a flatpak:
+
+`flatpak run --command={{sh}} {{com.example.app}}`