backend-*: updated READMEs

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/backend-dev-utils/README.md

@@ -1,5 +1,20 @@
-# backend-dev-utils
+# @backstage/backend-dev-utils
 
-Welcome to the backend-dev-utils package!
+**This package is EXPERIMENTAL, but we encourage use of it to add support for the new backend system in your own plugins**
 
-_This package is experimental._
+This package helps set up local development environments for Backstage backend packages.
+
+## Installation
+
+Add the library to your backend plugin or module package:
+
+```bash
+# From your Backstage root directory
+yarn add --cwd plugins/<plugin>-backend @backstage/backend-dev-utils
+```
+
+## Documentation
+
+- [Backstage Readme](https://github.com/backstage/backstage/blob/master/README.md)
+- [Backstage Documentation](https://github.com/backstage/backstage/blob/master/docs/README.md)
+- [Backstage Backend System](https://backstage.io/docs/backend-system/)