chore: simplify plugin readmes, changelogs and manifest descriptions

plugins/sso/README.md

@@ -0,0 +1,30 @@
+# Single sign-on
+
+Sign in with an OpenID Connect provider, GitHub or Google. Each provider gets its own button on the login screen.
+
+## Features
+
+- Sign in with any OpenID Connect provider, GitHub or Google.
+- Each provider gets its own button on the login screen.
+- Make members of an admin group Termix admins, read from a group claim.
+- Supports back-channel logout.
+
+## Settings
+
+### Admin
+
+- Providers: add a provider, then register the redirect URI it shows with your identity provider. Providers set up before 2.9 keep the old redirect URI until you turn it off.
+
+## Permissions
+
+- `sso.manage`: Add, edit and remove SSO providers. Only admins have it by default.
+
+## Development
+
+```bash
+npm run build      # build into dist/
+npm run test       # run this plugin's tests
+npm run typecheck  # type-check this plugin
+```
+
+See `packages/plugin-sdk/ARCHITECTURE.md` for the plugin contract.