Document i18n markup and help overlay

Add the missing legalNotice parameter to the config table.
Describe how translations resolve keys, which markup the
renderer accepts, and how the OS-keyed help dialog works.

README.md

@@ -14,6 +14,7 @@ Rename `assets/config.json.sample` to `assets/config.json`.
 | `jitsiLauncher` | Domain of this Jitsi launcher. Used for the meeting URLs created by the meeting creator (Nextcloud, adhoc link). |
 | `jitsiHost` | Jitsi domain. Used for the browser fallback URL, the desktop protocol URL and the UID of generated ICS files. |
 | `nextcloudBase` | Nextcloud instance for calendar event creation. The "Create in Nextcloud Calendar" button is only shown if this is set. |
+| `legalNotice` | URL of the "Legal Notice" link in the navbar. The link stays hidden if unset. |
 | `allowAdhocMeetings` | Whether adhoc meetings are allowed. The "Create Adhoc Link" button is only shown if this is `true`. |
 | `launchTimeout` | Timeout in ms before the browser fallback is shown after trying to start the jitsi-meet-electron client. |
 | `backgroundImage` | Path to the page background image. Empty: no background. |
@@ -21,6 +22,25 @@ Rename `assets/config.json.sample` to `assets/config.json`.
 | `favicons` | Paths to the page icons: `ico` (fallback icon), `svg` (icon), `appleTouch` (Apple touch icon). The values from `launch.html` are kept if a key is missing. |
 | `downloads` | Download URLs for the jitsi-meet clients, shown in the fallback view per detected OS: `windows`, `macos`, `linux`, `ios`, `android`. |
 
+## Translations
+
+All texts live in `assets/i18n.json`, one object per language
+(`en`, `de`, `fr`, `zh`). Elements carry the key in `data-i18n`
+(dots descend into nested objects), inputs in `data-i18n-placeholder`.
+
+Translations may contain `<kbd>`, `<b>` and `<i>` markup (no
+nesting). The renderer builds only these whitelisted elements;
+other tags render literally and never execute.
+
+## Help overlay
+
+The "Help" button in the navbar opens a dialog with
+camera/microphone hints. It only shows on the detected OS.
+The texts live under `meetingPrivacySettings` in
+`assets/i18n.json`, keyed by OS (`windows`; `macos`, `linux`,
+`ios` and `android` can follow). The dialog width is defined
+in `dialog.privacy` (`assets/css/launch.css`).
+
 ## Third-party assets
 
 - `assets/lib/ua-parser.min.js` — [ua-parser-js](https://github.com/faisalman/ua-parser-js) v2.0.10, © Faisal Salman, licensed under AGPL-3.0.