Merge pull request #175 from Pennycook/docs/rsp-files

Recommend using cmake -G Ninja in the tutorial

Author: Pennycook

docs/source/compilation-databases.rst

@@ -54,11 +54,19 @@ obtain a compilation database for the CPU:
 .. code :: sh
 
     $ mkdir build-cpu
-    $ cmake ../
+    $ cmake -G Ninja ../
     $ ls
 
     CMakeCache.txt  CMakeFiles  Makefile  cmake_install.cmake  compile_commands.json
 
+.. tip::
+    Using the "Ninja" generator is not required, but is often faster and can
+    improve the quality of CBI's results. Other generators (such as "Unix
+    Makefiles") may use response (:code:`.rsp`) files to pass command-line
+    options, and any options passed this way will not be respected by CBI.
+    You may need to install Ninja on your system (e.g., with :code:`pip install
+    ninja` or similar).
+
 This :code:`compile_commands.json` file includes all the commands required to
 build the code, corresponding to the commands that would be executed if we were
 to actually run :code:`make`.