Check for community installation (#2692)

Related ##1953

## Checklist

- [/] I have added
[tests](https://www.cursorless.org/docs/contributing/test-case-recorder/)
- [/] I have updated the
[docs](https://github.com/cursorless-dev/cursorless/tree/main/docs) and
[cheatsheet](https://github.com/cursorless-dev/cursorless/tree/main/cursorless-talon/src/cheatsheet)
- [/] I have not broken the cheatsheet

---------

Co-authored-by: Pokey Rule <[email protected]>

src/check_community_repo.py

@@ -0,0 +1,36 @@
+from talon import app, registry
+
+required_captures = [
+    "number_small",
+    "user.any_alphanumeric_key",
+    "user.formatters",
+    "user.ordinals_small",
+]
+
+required_actions = [
+    "user.homophones_get",
+    "user.reformat_text",
+]
+
+
+def on_ready():
+    missing_captures = [
+        capture for capture in required_captures if capture not in registry.captures
+    ]
+    missing_actions = [
+        action for action in required_actions if action not in registry.actions
+    ]
+    errors = []
+    if missing_captures:
+        errors.append(f"Missing captures: {', '.join(missing_captures)}")
+    if missing_actions:
+        errors.append(f"Missing actions: {', '.join(missing_actions)}")
+    if errors:
+        print("\n".join(errors))
+        app.notify(
+            "Please install the community repository",
+            body="https://github.com/talonhub/community",
+        )
+
+
+app.register("ready", on_ready)