fix(docs): repoint references to the relocated contributing guide (#115)

fix(docs): repoint references to the relocated contributing guide

The guide moved to .github/CONTRIBUTING.md; these references still
resolved
against the old root location and 404 from where they are written.
Rewritten
using the correct relative depth.

- `README.adoc`: CONTRIBUTING.md -> .github/CONTRIBUTING.md
- `ROADMAP.adoc`: CONTRIBUTING.md -> .github/CONTRIBUTING.md

Author: hyperpolymath

README.adoc

@@ -428,7 +428,7 @@ See link:ROADMAP.adoc[ROADMAP.adoc] for planned features including:
 
 == Contributing
 
-Contributions welcome. See link:CONTRIBUTING.md[CONTRIBUTING.md] for guidelines.
+Contributions welcome. See link:.github/CONTRIBUTING.md[CONTRIBUTING.md] for guidelines.
 
 This project follows the Rhodium Standard Repository (RSR) conventions.
 

ROADMAP.adoc

@@ -574,7 +574,7 @@ The following are explicitly out of scope:
 
 == Contributing
 
-See link:CONTRIBUTING.md[CONTRIBUTING.md] for contribution guidelines.
+See link:.github/CONTRIBUTING.md[CONTRIBUTING.md] for contribution guidelines.
 
 Priority areas for contribution: