chore: simplify plugin readmes, changelogs and manifest descriptions

plugins/webauthn/README.md

@@ -0,0 +1,19 @@
+# Passkeys
+
+Sign in with a passkey or security key instead of a password. A passkey that checks your PIN or fingerprint also counts as a second factor.
+
+## Features
+
+- Sign in with a passkey or security key instead of a password.
+- A passkey that checks your PIN or fingerprint also counts as a second factor.
+- Add more than one passkey, including synced ones.
+
+## 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.