docs: add contributor guide local development setup

docs/README.md

@@ -1,4 +1,21 @@
 # Documentation
 
-- [Using the AWS Provider](https://registry.terraform.io/providers/hashicorp/aws/latest/docs)
-- [AWS Provider contributing guide](https://hashicorp.github.io/terraform-provider-aws/)
+This directory contains documentation for the [Terraform AWS Provider Contributor Guide](https://hashicorp.github.io/terraform-provider-aws/). Resource and data source documentation is located in the [`website`](../website/) directory and available in the [Terraform Registry](https://registry.terraform.io/providers/hashicorp/aws/latest/docs).
+
+## Local Development
+
+To serve the contributing guide locally, [`mkdocs`](https://www.mkdocs.org/user-guide/installation/) and the [`mkdocs-material`](https://github.com/squidfunk/mkdocs-material#quick-start) extension must be installed. Both require Python and `pip`.
+
+```console
+% pip3 install mkdocs
+```
+
+```console
+% pip3 install mkdocs-material
+```
+
+Once installed, the documentation can be served from the root directory:
+
+```console
+% mkdocs serve
+```