Clang: Add README

Change-Id: Ib79cfa43713269e01eea196e035e01afcdd66e12
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/clangcodemodel/README

@@ -0,0 +1,65 @@
+The ClangCodeModel plugin
+=========================
+
+The ClangCodeModel plugin integrates the clang frontend into Qt Creator. Clang
+is "a C language family frontend for LLVM". You can find more information at
+http://clang.llvm.org/.
+
+At the time of writing the plugin can replace the following functionality of
+the built-in code model:
+    * Highlighting
+    * Completion
+
+All other functionality relies on the built-in code model (indexing, quick
+fixes, follow symbol, find usages, ...).
+
+Setup
+=====
+
+Compile the plugin
+------------------
+
+1. Get libclang
+
+You need to have libclang (and thus llvm) installed on your system. Either
+build llvm/clang yourself [1], install some ready-to-use package [2] or use the
+package manager of your system.
+
+    [1] http://clang.llvm.org/get_started.html
+        See http://llvm.org/docs/GettingStarted.html#git-mirror for git mirrors.
+    [2] http://llvm.org/releases/ or http://llvm.org/builds/
+
+If you are building llvm/clang yourself, make sure to build it in release mode.
+
+2. Set LLVM_INSTALL_DIR and (re)build Qt Creator
+
+Point the LLVM_INSTALL_DIR variable to the build/installation directory of
+llvm, e.g.:
+
+    Installed via package manager on GNU/Linux:
+        LLVM_INSTALL_DIR=/usr/lib/llvm-3.4
+    Manually build on Unix in release mode:
+        LLVM_INSTALL_DIR=$HOME/llvm-build/Release+Asserts
+    Installed a snapshot on Windows:
+        LLVM_INSTALL_DIR=C:\llvm
+
+Set the variable either as part of the build environment or pass it directly to
+qmake and rebuild Qt Creator. Watch out for a message like
+
+    Project MESSAGE: Building ClangCodeModel plugin with Clang from /usr/lib/llvm-3.4
+    Project MESSAGE:   INCLUDEPATH += /usr/lib/llvm-3.4/include
+    Project MESSAGE:   LIBS += -L/usr/lib/llvm-3.4/lib -lclang
+
+This indicates that the ClangCodeModel plugin will be build.
+
+Enable the plugin
+-----------------
+
+Enable the "ClangCodeModel" plugin in the dialog "Menu: Help -> About Plugins"
+and restart Qt Creator.
+
+Select the file types you want to use the ClangCodeModel for in "Menu: Tools ->
+Options -> C++ -> Tab: Code Model". For the next opened file matching the
+selected file types the ClangCodeModel will be used (see limitations at the
+start of this README).
+