Fix contribution link in README.adoc and add a link to repository map

Fixing broken link to contribution guidelines.

Adding a link to the high-level diagrams including module, library dependency and others at (https://sourcespy.com/github/springcloudspringcloudgateway/). Built directly from source and updated on schedule. Intended to simplify developer's introduction to the project. In the spirit of transparency - I am the author of the diagrams. Hope contributors find it useful.

docs/src/main/asciidoc/README.adoc

@@ -25,4 +25,4 @@ include::https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/main/
 [[contributing]]
 = Contributing
 
-include::https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/main/docs/src/main/asciidoc/contributing.adoc[]
+include::https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/main/docs/modules/ROOT/partials/contributing.adoc[]