[docs] Rename to permit wider variety of content.

I don't want to rule out the possibility of linking to e.g. interesting
blog posts about uses of Clang, so avoid restricting the content to
"projects".

This breaks URL compatibility, but this document was committed less than
an hour ago so hopefully nobody has linked to it yet.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175535 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ExternalProjectsUsingClang.rst → docs/ExternalClangExamples.rst

-=============================
-External Projects Using Clang
-=============================
+=======================
+External Clang Examples
+=======================
 
 Introduction
 ============

docs/index.rst

@@ -30,7 +30,7 @@ Using Clang as a Library
    :maxdepth: 1
 
    Tooling
-   ExternalProjectsUsingClang
+   ExternalClangExamples
    IntroductionToTheClangAST
    LibTooling
    LibFormat