Update AST matchers tutorial to use monorepo layout
Update AST matchers tutorial to use monorepo layout

The docs were inconsistent: requesting the user to clone the monorepo,
and then continuing with the `llvm/tools/clang` layout.

Follow-up to a question on cfe-dev:
http://lists.llvm.org/pipermail/cfe-dev/2019-June/062518.html

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@362683 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang