Update cheatsheets

tldr/linux/flatpak-mask

@@ -0,0 +1,21 @@
+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# flatpak mask
+
+> Mask out updates and automatic installation.
+> More information: <https://docs.flatpak.org/en/latest/flatpak-command-reference.html#flatpak-mask>.
+
+- Ignore updates for a specific flatpak:
+
+`flatpak mask {{com.example.app}}`
+
+- Undo ignore updates:
+
+`flatpak mask --remove {{com.example.app}}`
+
+- List all currently masked patterns:
+
+`flatpak mask {{--system|--user}}`