[Docs] Add LLVM for Grad Students to Contributing page.

[fhahn]

Summary

I think Adrian Sampson's blog post provides a good and relatively
up-do-date introduction to LLVM. I am not sure what the policy about
including links to third-party sites is, but I think this post could be
helpful for people wanting to get started with LLVM.

[asb]

I don't see a problem in linking to an external source personally, and think that Adrian's blog post is fantastic - does anyone have objections?

[fhahn]

Thanks Alex. Adding Renato too, in case he knows if I missed someone who could have an opinion on this.

[rengolin]

We want to be consistent and have all internal docs clustered first. I don't see a problem in having external docs listed at the end, though.

[fhahn]

Thanks Renato. I moved the aosabook to the end too. I think LLVM For Grad Students is more up to date.

[rengolin]

LGTM, thanks!

llvm/trunk/docs/Contributing.rst

 
 
 Helpful Information About LLVM
 ==============================
 :doc:`LLVM's documentation <index>` provides a wealth of information about LLVM's internals as
 well as various user guides. The pages listed below should provide a good overview
 of LLVM's high-level design, as well as its internals:
 
-`Intro to LLVM`__
-  Book chapter providing a compiler hacker's introduction to LLVM.
-
-  .. __: http://www.aosabook.org/en/llvm.html
-
 :doc:`GettingStarted`
    Discusses how to get up and running quickly with the LLVM infrastructure.
    Everything from unpacking and compilation of the distribution to execution
    of some tools.
 
 :doc:`LangRef`
   Defines the LLVM intermediate representation.
 
 :doc:`ProgrammersManual`
   Introduction to the general layout of the LLVM sourcebase, important classes
   and APIs, and some tips & tricks.
 
 :ref:`index-subsystem-docs`
   A collection of pages documenting various subsystems of LLVM.
 
+`LLVM for Grad Students`__
+  This is an introduction to the LLVM infrastructure by Adrian Sampson. While it
+  has been written for grad students, it provides  a good, compact overview of
+  LLVM's architecture, LLVM's IR and how to write a new pass.
 
+  .. __: http://www.cs.cornell.edu/~asampson/blog/llvm.html
+
+`Intro to LLVM`__
+  Book chapter providing a compiler hacker's introduction to LLVM.
+
+  .. __: http://www.aosabook.org/en/llvm.html
 
 .. _Developer's List (llvm-dev): http://lists.llvm.org/mailman/listinfo/llvm-dev
 .. _irc.oftc.net: irc://irc.oftc.net/llvm
 .. _beginner keyword: https://bugs.llvm.org/buglist.cgi?bug_status=NEW&bug_status=REOPENED&keywords=beginner%2C%20&keywords_type=allwords&list_id=130748&query_format=advanced&resolution=---
 .. _bug tracker: https://bugs.llvm.org
 .. _clang-format-diff.py: https://reviews.llvm.org/source/clang/browse/cfe/trunk/tools/clang-format/clang-format-diff.py
 .. _git-clang-format: https://reviews.llvm.org/source/clang/browse/cfe/trunk/tools/clang-format/git-clang-format
 .. _LLVM's Phabricator: https://reviews.llvm.org/
 .. _LLVM's Open Projects page: https://llvm.org/OpenProjects.html#what
 .. _LLVM Developer's mailing list: http://lists.llvm.org/mailman/listinfo/llvm-dev