Group help texts under a help key

meetingPrivacySettings nests one level deeper under help.
The umbrella makes room for further help topics and allows
contextualizing which help a visible view offers. All
data-i18n references follow; no logic changes.

README.md

@@ -36,10 +36,13 @@ other tags render literally and never execute.
 
 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`).
+All help texts live under `help` in `assets/i18n.json`,
+grouped by topic; the overlay uses
+`help.meetingPrivacySettings`, keyed by OS (`windows`;
+`macos`, `linux`, `ios` and `android` can follow). Further
+topics can extend `help` and be contextualized per visible
+view. The dialog width is defined in `dialog.privacy`
+(`assets/css/launch.css`).
 
 ## Third-party assets