Add clearer language and options to Arcanist install guides

Summary: Fixes T12315. Reworks the copy placement a little, adds more links.

Test Plan: Read in sandbox

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12315

Differential Revision: https://secure.phabricator.com/D17413

src/docs/user/userguide/arcanist_mac_os_x.diviner

@@ -9,6 +9,7 @@ You need to install:
 
   - PHP, which should be installed by default.
   - Arcanist itself, see @{article:Arcanist User Guide}.
+  or @{article:Arcanist Quick Start}
   - SVN, Git, or Mercurial.
 
 Then, configure:

src/docs/user/userguide/arcanist_quick_start.diviner

@@ -4,16 +4,15 @@
 Quick guide to getting Arcanist working for a new project.
 
 This is a summary of steps to install Arcanist, configure a project for use with
-it, and run `arc` to send changes for review.
-
-= Install Arcanist =
-
-For detailed instructions on installing Arcanist, see
-@{article:Arcanist User Guide}.
+it, and run `arc` to send changes for review. For detailed instructions on
+installing Arcanist, see @{article:Arcanist User Guide}. OS specific guides
+are also available.
 
   - For Mac OS X, see @{article:Arcanist User Guide: Mac OS X}.
   - For Windows, see @{article:Arcanist User Guide: Windows}.
 
+= Installing Arcanist =
+
 First, install dependencies:
 
   - Install PHP.

src/docs/user/userguide/arcanist_windows.diviner

@@ -17,6 +17,7 @@ into issues.
 You need to install:
 
   - Arcanist itself, see @{article:Arcanist User Guide}.
+  or @{article:Arcanist Quick Start}.
   - PHP (see "Detailed PHP Install Instructions" below).
   - SVN, Git, or Mercurial.