chore: rework plugin readmes, json changelogs and standalone repo setup

plugins/alerts/CONTRIBUTING.md

@@ -0,0 +1,27 @@
+# Contributing to Alerts
+
+## Development
+
+```bash
+npm run build      # build into dist/
+npm run test       # run this plugin's tests
+npm run typecheck  # type-check this plugin
+npm run validate   # check manifest.json
+npm run format     # format the code with Prettier
+```
+
+## Settings
+
+### Admin
+
+- **Termix announcements:** show news from the Termix team in everyone's inbox
+- **Keep alerts for (days):** older alerts are removed from every inbox
+- **SMTP server, port, TLS, username, password and from address:** needed for email channels. Leave the server empty to turn email off
+
+### User
+
+- **Alert popups:** all alerts, warnings and critical, critical only, or none
+
+## Permissions
+
+- `alerts.use`: get alerts in the inbox and send them to your own channels. Admins and users have it by default.