Remove mention of contribution guidelines in README

Earlier versions of the documentation had contribution guidelines but they were taken down because the system design and architecture was and still is under very frequent revision

Author: hmakelin

README.md

@@ -97,7 +97,7 @@ gnc stop
 # Documentation
 
 See the [latest developer documentation][6] for information on how to setup a local environment for GISNav development,
-for code examples and API documentation, and for contribution guidelines.
+for code examples and API documentation, and integration examples.
 
 [6]: https://hmakelin.github.io/gisnav