Better readme

README.md

@@ -1,4 +1,30 @@
 # docs-base
 
-# This is the source for docs/docs-base. Push to that location to ensure that
-# the production image gets your update :)
+This is the source for docs/docs-base.
+
+The docs-base Dockerfile includes:
+
+- The GitHub Pages environment (w/Jekyll)
+- nginx
+- Builds of all previous versions of Docker's documentation
+
+Having this large amount of stuff that stays relatively static in a base image
+helps keep build times for the docs low as we can use Docker Cloud's caching
+when running auto-builds out of GitHub.
+
+While you would only see the docs archives by doing so, you can run docs-base
+locally and peruse by running:
+
+```
+docker run -ti -p 4000:4000 docs/docker.github.io:docs-base
+```
+
+The contents of docs-base will then be viewable in your browser at
+`localhost:4000`.
+
+## Reasons to update this branch
+
+- Changing the nginx configuration
+- Publishing a new docs archive, or anything else that stays static between
+  doc builds.
+- Updating the GitHub Pages version used in production to a newer release