Make the tutorial easier to compile by adding in some of the details.

Patch by Béatrice Creusillet.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176434 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LibASTMatchersTutorial.rst

@@ -261,6 +261,11 @@ from a ``ClangTool``. More code!
 Add the following to ``LoopConvert.cpp``:
 
 ::
+      #include "clang/ASTMatchers/ASTMatchers.h"
+      #include "clang/ASTMatchers/ASTMatchFinder.h"
+
+      using namespace clang;
+      using namespace clang::ast_matchers;
 
       StatementMatcher LoopMatcher =
         forStmt(hasLoopInit(declStmt(hasSingleDecl(varDecl(