README updates (Exawind#1271)

README.md

@@ -1,6 +1,6 @@
 # AMR-Wind 
 
-[User manual](https://exawind.github.io/amr-wind) | [API docs](https://exawind.github.io/amr-wind/api_docs) | [Nightly test dashboard](http://my.cdash.org/index.php?project=Exawind) 
+[Documentation](https://exawind.github.io/amr-wind) | [API docs](https://exawind.github.io/amr-wind/api_docs) | [Nightly test dashboard](http://my.cdash.org/index.php?project=Exawind) 
 
 [![Powered by AMReX](https://amrex-codes.github.io/badges/powered%20by-AMReX-red.svg)](https://amrex-codes.github.io/amrex/) [![Build Status](https://github.com/Exawind/amr-wind/workflows/AMR-Wind-CI/badge.svg)](https://github.com/Exawind/amr-wind/actions) [![OpenSSF Best Practices](https://www.bestpractices.dev/projects/9284/badge)](https://www.bestpractices.dev/projects/9284)
 
@@ -40,9 +40,10 @@ objectives:
 
 ## Documentation
 
-Documentation is organized into a [user manual](https://exawind.github.io/amr-wind)
-and a developer-focused [API
-documentation](https://exawind.github.io/amr-wind). You can either
+Documentation is available at https://exawind.github.io/amr-wind, which 
+includes a walkthrough tutorial, a user manual, notes on theory,
+and tips for developers. We also provide a developer-focused [API
+documentation](https://exawind.github.io/amr-wind/api_docs). You can either
 browse the docs online by following the links, or you can generate them locally
 after downloading the code. Please follow the instructions in user manual to
 build documentation locally.