docs: added commitlint-gitlab-ci in community docs

[dmoonfire]

Description

Added a link to a community tool for working with Gitlab CI without throwing errors.

Motivation and Context

This addresses #885 (comment) which references a problem when commitlint is first run on a Gitlab CI and blows up because it cannot read the SHA. After a number of discussions, I wrote a little utility to encapsulate the last "best" set of scripts to make it easy to work with Gitlab CI.

Usage examples

npx commitlint-gitlab-ci -x @commitlint/config-conventional

How Has This Been Tested?

The documentation was just a copy of the link. The utility was manually tested on a number of Gitlab CI.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[escapedcat]

Thanks