feat: appimage package script

revert: flutter lock file

appimage/README.md

@@ -0,0 +1,20 @@
+# How to build and run RustDesk in AppImage
+
+Begin by installing `appimage-builder` and predependencies mentioned in official website.
+
+Assume that `appimage-builder` is setup correctly, run commands below, `bash` or `zsh` is recommended:
+
+```bash
+cd /path/to/rustdesk_root
+./build_appimage.py
+```
+
+After a success package, you can see the message in console like:
+
+```shell
+INFO:root:AppImage created successfully
+```
+
+The AppImage package is shown in `./appimage/RustDesk-VERSION-TARGET_PLATFORM.AppImage`. 
+
+Note: AppImage version of rustdesk is an early version which requires more test. If you find problems, please open an issue.