docs: Add app updater dev env vars to readme

ui/desktop/README.md

@@ -65,6 +65,16 @@ To run as a desktop app:
 The Boundary CLI is downloaded and extracted to `electron-app/cli/` folder as part of
 build. CLI version is defined in `electron-app/config/cli.js`.
 
+#### Environment Variables
+
+These environment variables may be used to customized the build.
+
+| Variable | Description |
+| -------- | ----------- |
+| `DEBUG_APP_UPDATER` | Enable to debug app updater feature. Must be enabled for all `APP_UPDATER_*` variables to be used. |
+| `APP_UPDATER_LATEST_VERSION_TAG` | Version string for comparison with current release version. |
+| `APP_UPDATER_LATEST_VERSION_LOCATION` | Location of app release to use for updating client. Can be a filepath or url. |
+
 ### Building for Production
 
 Before executing a build, be sure to set any environment variables necessary

ui/desktop/electron-app/src/app-updater.js

@@ -46,7 +46,7 @@ const downloadAndInstallUpdate = async (version) => {
     let configPath;
     if (debug) {
       // Support hosted url and file paths
-      const location = process.env.LATEST_VERSION_LOCATION;
+      const location = process.env.APP_UPDATER_LATEST_VERSION_LOCATION;
       configPath = createAppUpdaterConfig(
         location.match(/^https/i) ? location : `file://${location}`,
         version,
@@ -90,7 +90,7 @@ module.exports = {
   run: async () => {
     let latestVersion;
     if (debug) {
-      latestVersion = process.env.LATEST_VERSION_TAG;
+      latestVersion = process.env.APP_UPDATER_LATEST_VERSION_TAG;
     } else {
       latestVersion = await findLatestVersion(releasesUrl);
     }