Update README to include contributor information.

Author: Stephen Tramer

README.md

@@ -1,3 +1,18 @@
+# Azure CLI documentation
+
+This repository hosts the documentation source for the Azure CLI, published on [docs.microsoft.com](https://docs.microsoft.com/cli/azure/).
+
+## Public contributions
+
+We welcome public contributions to the Azure CLI documentation! There are two types of documentation hosted in this repository,
+with different workflows:
+
+* To submit a change for _conceptual_ documentation (content in the `docs-ref-conceptual` directory) make a pull request against
+  this repository.
+* To submit a change for _reference_ documentation (all other documentation), please make a pull request against
+  [azure/azure-cli](https://github.com/azure/azure-cli). This reference is generated from the source code, and is also used in
+  the command-line `-h` help.
+
 ## Microsoft Open Source Code of Conduct
 
 This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/).