Add description for account notification setting

[yostyle]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

Motivation and context

#1107

Screenshots / GIFs

Tests

• Step 1
• Step 2
• Step ...

Tested devices

• Physical
• Emulator
• OS version(s):

Checklist

• Changes has been tested on an Android device or Android emulator with API 21
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/tchapgouv/tchap-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request includes a new file under ./changelog.d. See https://github.com/tchapgouv/tchap-android/blob/develop/CONTRIBUTING.md#changelog
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR
• If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()