Add documentation for Phabricator.

[klimek]

Summary

Please let me know if this is the wrong place for the docs, or if I'm missing
important stuff. Also, I hope I got the right spot to hook it in.

[klimek]

• typos

[silvas]

This is a good starting point. There are a number of modifications that I would like to make, especially to the general organization, but let's get this checked in.

[klimek]

Submitted as r165736

docs/DeveloperPolicy.rst

 #. Code review can be an iterative process, which continues until the patch is
    ready to be committed.
 
 Developers should participate in code reviews as both reviewers and
 reviewees. If someone is kind enough to review your code, you should return the
 favor for someone else.  Note that anyone is welcome to review and give feedback
 on a patch, but only people with Subversion write access can approve it.
 
+There is a web based code review tool that can optionally be used
+for code reviews. See the documentation on `Code Reviews with
+Phabricator <Phabricator.html>`_.
+
 Code Owners
 -----------
 
 The LLVM Project relies on two features of its process to maintain rapid
 development in addition to the high quality of its source base: the combination
 of code review plus post-commit review for trusted maintainers.  Having both is
 a great way for the project to take advantage of the fact that most people do
 the right thing most of the time, and only commit patches without pre-commit

docs/Phabricator.rst

+.. _Phabricator:
+.. _LLVM's Phabricator: http://llvm-reviews.chandlerc.com
+.. _Code Repository Browser: http://llvm-reviews.chandlerc.com/diffusion/
+.. _Arcanist Quick Start: http://www.phabricator.com/docs/phabricator/article/Arcanist_Quick_Start.html
+.. _Arcanist User Guide: http://www.phabricator.com/docs/phabricator/article/Arcanist_User_Guide.html
+
+
+=============================
+Code Reviews with Phabricator
+=============================
+
+.. contents::
+  :local:
+
+If you prefer to use a web user interface for code reviews,
+you can now submit your patches for Clang and LLVM at
+`LLVM's Phabricator`_.
+
+Sign up
+-------
+
+Sign up with one of the supported OAuth account types. If
+you use your Subversion user name as Phabricator user name,
+Phabricator will automatically connect your submits to your
+Phabricator user in the `Code Repository Browser`_.
+
+
+Requesting a review via the command line
+----------------------------------------
+
+Phabricator has a tool called *Arcanist* to upload patches from
+the command line. To get you set up, follow the
+`Arcanist Quick Start`_ instructions.
+
+You can learn more about how to use arc to interact with
+Phabricator in the `Arcanist User Guide`_.
+
+Requesting a review via the web interface
+-----------------------------------------
+
+The tool to create and review patches in Phabricator is called
+*Differential*.
+
+Note that you can upload patches created through various diff tools,
+including git and svn. To make reviews easier, please always include
+**as much context as possible** with your diff! Don't worry, Phabricator
+will automatically send a diff with a smaller context in the review
+email, but having the full file in the web interface will help the
+reviewer understand your code.
+
+To get a full diff, use one of the following commands (or just use Arcanist
+to upload your patch):
+
+* git diff -U999999 other-branch
+* svn diff --diff-cmd=diff -x -U999999
+
+To upload a new patch:
+
+* Click *Differential*.
+* Click *Create Revision*.
+* Paste the text diff or upload the patch file.
+  Note that TODO
+* Leave the drop down on *Create a new Revision...* and click *Continue*.
+* Enter a descriptive title and summary; add reviewers and mailing
+  lists that you want to be included in the review. If your patch is
+  for LLVM, cc llvm-commits; if your patch is for Clang, cc cfe-commits.
+* Click *Save*.
+
+To submit an updated patch:
+
+* Click *Differential*.
+* Click *Create Revision*.
+* Paste the updated diff.
+* Select the review you want to from the *Attach To* dropdown and click
+  *Continue*.
+* Click *Save*.
+
+Reviewing code with Phabricator
+-------------------------------
+
+Phabricator allows you to add inline comments as well as overall comments
+to a revision. To add an inline comment, select the lines of code you want
+to comment on by clicking and dragging the line numbers in the diff pane.
+
+You can add overall comments or submit your comments at the bottom of the page.
+
+Phabricator has many useful features, for example allowing you to select
+diffs between different versions of the patch as it was reviewed in the
+*Revision Update History*. Most features are self descriptive - explore, and
+if you have a question, drop by on #llvm in IRC to get help.
+
+Status
+------
+
+Currently, we're testing Phabricator for use with Clang/LLVM. Please let us
+know whether you like it and what could be improved!