Add sserpolar/devdocs-lookup to Related Projects

[sserpolar]

Adds a browser extension to the Related Projects table.

sserpolar/devdocs-lookup adds a single
"Search DevDocs for ..." item to the browser right-click menu. Selecting an identifier on
any page opens the matching DevDocs entry in a small top-level window, leaving the page you
were reading untouched.

This is the case the maintainer described as out of scope for DevDocs itself in #1518:

Changing the context menu requires a browser extension ... thus, is out of scope of devdocs.

A few things that seemed worth stating explicitly:

• It does not embed DevDocs. The window is a normal top-level browser window pointed at
  devdocs.io, opened with chrome.windows.create({type:"popup"}). Nothing is framed and
  nothing is modified. Because it stays first-party, the user's own enabled documentation
  sets, theme and downloaded offline data all remain in effect. (An earlier iframe-based
  version was abandoned precisely because DevDocs preferences live in SameSite=Lax cookies
  that a cross-site frame cannot read.)
• It cannot read page content. The manifest declares one permission, contextMenus, with
  no host permissions, no content scripts, no activeTab and no scripting. The only data it
  ever receives is the selectionText Chrome hands it with the menu click, which goes into a
  URL fragment.
• MIT licensed. Published on the
  Chrome Web Store
  and Edge Add-ons.

The row is inserted in description-alphabetical order per the
<!-- table is sorted by description --> comment, between "Brackets extension" and
"Electron application".

[mo74m3ed]

@mohammed