doc: modules: document recommendations

Update Modules (External projects) documentation to:

- Recommend explicitly setting the module name in module.yml
- Recommend exposing module-provided headers with an include
  pathname beginning with the module-name.

Fixes #49766

Signed-off-by: Gregory SHUE <gregory.shue@legrand.com>
Co-authored-by: Stephanos Ioannidis <root@stephanos.io>