Mapping model documentation is needed in OSCAL Pages #74
Description
Mapping model documentation is necessary.
[ ] Page src/content/resources/concepts/layer/control/_index.md must be updated
[ ] Subdirectory https://pages.nist.gov/OSCAL/concepts/layer/control/mapping/ needs to be created with the file _index.md (see src/content/resources/concepts/layer/control/catalog/_index.md as example)