Links in documentation are broken

[123Haynes]

Describe the bug

Currently the docs contain several links to https://goss.rocks. Those are all broken.
I assume most should be replaced with the appropriate links to https://goss.readthedocs.io/en/stable/
I'm happy to provide a PR to fix those if linking them to readthedocs.io is the prefered solution 😄

Broken Links:
https://github.com/goss-org/goss/blob/master/README.md?plain=1#L108-L109
https://github.com/goss-org/goss/blob/master/README.md?plain=1#L164
https://github.com/goss-org/goss/blob/master/README.md?plain=1#L196
https://github.com/goss-org/goss/blob/master/README.md?plain=1#L203
https://github.com/goss-org/goss/blob/master/README.md?plain=1#L209-L211
https://github.com/goss-org/goss/blob/master/README.md?plain=1#L346

https://github.com/goss-org/goss/blob/master/docs/gossfile.md?plain=1#L106
https://github.com/goss-org/goss/blob/master/docs/gossfile.md?plain=1#L115

https://github.com/goss-org/goss/blob/master/.github/ISSUE_TEMPLATE/feature_request.md?plain=1#L14

https://github.com/goss-org/goss/blob/master/.github/CONTRIBUTING.md?plain=1#L38

[dklimpel]

Related to:

• Final steps to new documentation #925