docs: create a new dev-tools directory

This directory will be a collecting point for documentation oriented around
development tools.  As a step toward ordering Documentation/ it's a small
one, but we have to start somewhere...
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/dev-tools/tools.rst

+================================
+Development tools for the kernel
+================================
+
+This document is a collection of documents about development tools that can
+be used to work on the kernel.  For now, the documents have been pulled
+together without any significant effot to integrate them into a coherent
+whole; patches welcome!
+
+.. class:: toc-title
+
+	   Table of contents
+
+.. toctree::
+   :maxdepth: 2
+

Documentation/index.rst

@@ -14,6 +14,7 @@ Contents:
    :maxdepth: 2
 
    kernel-documentation
+   dev-tools/tools
    media/media_uapi
    media/media_kapi
    media/dvb-drivers/index