Update variables' docs in the README

Author: TheAssassin

README.md

@@ -33,10 +33,13 @@ The official linuxdeploy AppImage ships with a fairly recent version of the plug
 
 linuxdeploy-plugin-appimage can be configured using environment variables.
 
-- `UPDATE_INFORMATION="..."`: embed [update information](https://github.com/AppImage/AppImageSpec/blob/master/draft.md#update-information) in the AppImage, and generate corresponding `.zsync` file
-- `SIGN=1`: set this variable to any value to enable signing of the AppImage
-- `SIGN_KEY=key_id`: GPG Key ID to use for signing. This environment variable is only used if `SIGN` is set.
-- `VERBOSE=1`: set this variable to any value to enable verbose output
-- `OUTPUT=filename`: change filename of resulting AppImage
-- `NO_APPSTREAM=1`: skip checking AppStream metadata for issues
-- `APPIMAGE_COMP=...`: compression algorithm appimagetool/mksquashfs should use (e.g., `xz`, `gzip`), see [appimagetool's repository](https://github.com/AppImage/AppImageKit/) for more information
+- `LDAI_UPDATE_INFORMATION="..."`: embed [update information](https://github.com/AppImage/AppImageSpec/blob/master/draft.md#update-information) in the AppImage, and generate corresponding `.zsync` file
+- `LDAI_GUESS_UPDATE_INFORMATION`: make appimagetool try to guess some update information (may or may not work, requires specific workflow and setup)
+- `LDAI_SIGN=1`: set this variable to any value to enable signing of the AppImage
+- `LDAI_SIGN_KEY=key_id`: GPG Key ID to use for signing. This environment variable is only used if `SIGN` is set.
+- `LDAI_VERBOSE=1`: set this variable to any value to enable verbose output
+- `LDAI_OUTPUT=filename`: change filename of resulting AppImage
+- `LDAI_NO_APPSTREAM=1`: skip checking AppStream metadata for issues
+- `LDAI_APPIMAGE_COMP=...`: compression algorithm appimagetool/mksquashfs should use (e.g., `xz`, `gzip`), see [appimagetool's repository](https://github.com/AppImage/AppImageKit/) for more information
+- `LINUXDEPLOY_OUTPUT_APP_NAME`: sets `APPIMAGETOOL_APP_NAME` to configure appimagetool's autogenerated filename prefix
+- `LINUXDEPLOY_OUTPUT_VERSION` or `LDAI_VERSION`: version number to pass to appimagetool (will be included in the root desktop file to be picked up by desktop integration tools and, if `$LDAI_OUTPUT` is not set, will be included in appimagetool's autogenerated output filename)