docs: Extend readme, more docs
Adds/updates docs.
Bug: 125, 129
Change-Id: I96b8bc07c3817d6b629e546f74c06d7345b3227e
diff --git a/pw_build/docs.rst b/pw_build/docs.rst
index cf92341..ce8d5e5 100644
--- a/pw_build/docs.rst
+++ b/pw_build/docs.rst
@@ -30,11 +30,16 @@
GN / Ninja
==========
-The common configuration for GN for all modules is in the ``BUILD.gn`` file.
-It contains ``config`` declarations referenced by ``BUILD.gn`` files in other
-modules.
+The GN / Ninja build system is the primary build system used for upstream
+Pigweed development, and is the most tested and feature-rich build system
+Pigweed offers.
-The module also provides some useful GN templates for build targets.
+This module's ``build.gn`` file contains a number of C/C++ ``config``
+declarations that are used by upstream Pigweed to set some architecture-agnostic
+compiler defaults. (See Pigweed's ``//BUILDCONFIG.gn``)
+
+pw_build also provides several useful GN templates that are used throughout
+Pigweed.
Templates
---------
@@ -142,6 +147,11 @@
CMake / Ninja
=============
+
+Pigweed's CMake support is provided primarily for projects that have an existing
+CMake build and wish to integrate Pigweed without switching to a new build
+system.
+
The following command generates Ninja build files in the out/cmake directory.
.. code:: sh
@@ -190,6 +200,9 @@
Bazel
=====
+
+Bazel is currently very experimental, and only builds for host.
+
The common configuration for Bazel for all modules is in the ``pigweed.bzl``
file. The built-in Bazel rules ``cc_binary``, ``cc_library``, and ``cc_test``
are wrapped with ``pw_cc_binary``, ``pw_cc_library``, and ``pw_cc_test``.