Adding more links from API docs to user guide

[maxrjones]

Description of the desired feature

#1044 added a link from the projection parameter to the projections user guide. I think it could be useful to add links from the API docs to the user guides for other parameters as well.

Here's a list of two of the most complicated common options and the related user guide pages.

• R (region) - user guide doc reference is /tutorials/regions; generated page is https://www.pygmt.org/dev/tutorials/regions.html
• B (frame) - user guide doc reference is /tutorials/frames; generated page is https://www.pygmt.org/dev/tutorials/frames.html

The associated API documentation for these parameters are in /pygmt/helpers/decorators.py. #1044 (in addition to the contributing docs) can be used as a guide.

Are you willing to help implement and maintain this feature? Yes, but I think this is a good first issue if someone new is interested.