pw_system: initial commit

- Added docs, and empty build files to get started.

Change-Id: Id3cadabfec7dc172b206e597371b30569e9e2c79
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/72840
Reviewed-by: Armando Montanez <amontanez@google.com>
Commit-Queue: Carlos Chinchilla <cachinchilla@google.com>
diff --git a/pw_system/docs.rst b/pw_system/docs.rst
new file mode 100644
index 0000000..439ea21
--- /dev/null
+++ b/pw_system/docs.rst
@@ -0,0 +1,7 @@
+.. _module-pw_system:
+
+=========
+pw_system
+=========
+.. warning::
+  Under construction, stay tuned!