Article description - update terminology

[tonisevener]

Fixes Phabricator ticket: https://phabricator.wikimedia.org/T261237

Notes

• I wasn't sure whether these changes earned a new localization key, but ultimately decided that just changing the English text will be enough. According to https://www.mediawiki.org/wiki/Localisation#Changing_existing_messages, it will still be marked as outdated on the TranslateWiki side for translators to re-check.

Test Steps

1. Confirm mentions of "title description" in the app have changed to "article description". These changes can be found in the alert view after tapping the first section edit button, the description editing onboarding modal, the description editing modal,
   and the "Learn more" modal.

Screenshots/Videos (if applicable)

Before:

After:

[staykids]

Didn't get to this one today so unassigning myself if it's holding anything up – otherwise, happy to jump back to it on Tuesday.

[staykids]

👍🏽 Looks good! I directly committed two minor fixes: removing extraneous space between an instance of "article description" in one string and after a couple of variable assignments.