include and locale-ready webtorrent description

[cezaraugusto]

• Auditors: @jonathansampson
• Fix Updated webtorrent description on extensions page #8208

Test Plan:

• Go to about:extensions
  • Webtorrent description should be Uses WebTorrent to display torrents directly in the browser. Supports torrent files and magnet links.
• Go to preferences -> extensions
  • Webtorrent description should be Uses WebTorrent to display torrents directly in the browser. Supports torrent files and magnet links.
• Other extensions descriptions on both places shouldn't be affected

[jonathansampson]

@cezaraugusto Looks good, but any reason not to include a description for Sync, Vimium at this time too?

[cezaraugusto]

for Sync is basically that it's not included on extensionsTab and UI doesn't look bad on about:extensions, and for Vimium because it's not yet included. For Vimium we can address once we allow it as an option for users.

[cezaraugusto]

I'll merge this as-is since it impacts UI on extTab but feel free to tag me for follow-ups regarding other extensions. btw I'm up to do for Sync as well once we have a description for that.

[feross]

LGTM