Fix typo in ogcapi-processes.rst

[C-Loftus]

The docs render "Shapely_" instead of linking to the Shapely link defined in the bottom of the rst file. This commit fixes that and properly links to https://shapely.readthedocs.io/ There seems to have been a minor syntax error here.

Contributions and licensing

(as per https://github.com/geopython/pygeoapi/blob/master/CONTRIBUTING.md#contributions-and-licensing)

• [X] I'd like to docs to pygeoapi. I confirm that my contributions to pygeoapi will be compatible with the pygeoapi license guidelines at the time of contribution
• [X] I have already previously agreed to the pygeoapi Contributions and Licensing Guidelines

[C-Loftus]

For reference, I previously fixed #1709 and am currently reading through the pygeoapi docs.

I wanted to submit any fixes as they came up so I didn't forget, but if you prefer larger PRs and don't like multiple small fixes like these, please let me know. Don't want to add labeling boilerplate for you each time.