intellij: add localconfig helper

Adds a little helper tool which merges a watcherTasks template with the local
project config. This restores the functionality lost in D658.

Also cured me of any remaining nostalgic feelings towards XML.

Test Plan:
Deleted all watchers, ran the script, re-opened project,
watchers are back and functional. Local watchers with the same name got
overwritten. Additional watchers were untouched.

X-Origin-Diff: phab/D661
GitOrigin-RevId: 83f7c1506476378145781c816d776fd451aed40c
diff --git a/README.md b/README.md
index 24f2cfb..7d6c2d3 100644
--- a/README.md
+++ b/README.md
@@ -48,3 +48,8 @@
 - Use _File → Import Bazel project_... to create a new project from `.bazelproject`.
 
 After running the first sync, everything should now resolve in the IDE, including generated code.
+
+It's strongly recommend to use our project presets for file watchers and other IDE features. Run this command and
+re-open the project in order to install them:
+
+    bazel run intellij/localconfig $(pwd)