Add Coding Conventions Section to Vector README

Although the convention of where to put conventions remains somewhat
contentious, the team's desired conventions for Desktop Improvments have
so far been, for the most part, general and could be useful for any
project our team owns (e.g. MobileFrontend, Minerva, etc).

Therefore, I added/made revisions to the
https://www.mediawiki.org/wiki/Reading/Web/Coding_conventions wiki page
as this seems the be the single source of truth of our team specific
conventions that span across repos.

This commit just links to these changes which follows the same pattern
as Minerva and MobileFrontend.

Additional Changes:

* Added installation section similar to Minerva Skin

Bug: T239269
Change-Id: I41c71fba1228086f1830d8bb0808227b62ebf5cd

README.md

@@ -1,10 +1,28 @@
 Vector Skin
 ========================
 
-Configuration options
----------------------
+Installation
+------------
 
-### $wgVectorPrintLogo
+See <https://www.mediawiki.org/wiki/Skin:Vector>
+
+Development
+-----------
+
+### Coding conventions
+
+We strive for compliance with MediaWiki conventions:
+
+<https://www.mediawiki.org/wiki/Manual:Coding_conventions>
+
+Additions and deviations from those conventions that are more tailored to this
+project are noted at:
+
+<https://www.mediawiki.org/wiki/Reading/Web/Coding_conventions>
+
+### Configuration options
+
+#### $wgVectorPrintLogo
 
 Logo used in print styles. Keys are `url`, `width`, and `height` (in
 pixels). Note that this solution only works correctly if the image