docs: fixed links for storage drivers

Signed-off-by: Ian Babrou <ibobrik@gmail.com>
(cherry picked from commit 824e7e8ae2)

Conflicts:
	docs/mkdocs.yml

Add environment variable override instructions

Signed-off-by: Richard Scothern <richard.scothern@gmail.com>
(cherry picked from commit 937c356585)

Fixing headings

Signed-off-by: Mary Anthony <mary@docker.com>
(cherry picked from commit 7c93c8c265)

Fixes Issue #471 with Publish

- Add sed to Dockerfile; this sed exists on publish script; breaks headings/nav in files without metadata
- Ensure sed runs over storage-driver/ subdir
- Add metadata to all the files (including specs) that don't have it; this ensures they display correctly on publish
- Implement the fix for the showing up in Github
- Update template with GITHUB IGNORES

Signed-off-by: Mary Anthony <mary@docker.com>
(cherry picked from commit 68c0682e00)

docs/configuration.md

@@ -1,6 +1,8 @@
+<!--GITHUB
 page_title: Configure a Registry
 page_description: Explains how to deploy a registry 
 page_keywords: registry, service, images, repository
+IGNORES-->
 
 
 # Registry Configuration Reference
@@ -9,6 +11,18 @@ You configure a registry server using a YAML file. This page explains the
 configuration options and the values they can take. You'll also find examples of
 middleware and development environment configurations.
 
+## Overriding configuration options
+Environment variables may be used to override configuration parameters other than 
+version.  To override a configuration option, create an environment variable named 
+REGISTRY\_variable_ where *variable* is the name of the configuration option.
+
+e.g 
+```
+REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY=/tmp/registry/test
+```
+
+will set the storage root directory to `/tmp/registry/test`
+
 ## List of configuration options
 
 This section lists all the registry configuration options. Some options in