user-facing CLI to run LM checks on local private repositories

[ilveroluca]

While LM can execute its checks on repositories hosted on GitHub, users have requested the ability to manually execute the same checks on their local repositories.

This feature is available for development and testing. The issue here is for making that feature accessible to common users.

At the very least, this implies documenting the CLI in the online docs. Not sure whether we also need to do something on the software side (given that the CLI is currently only tailed for developers, some things might need to be streamlined).

[ilveroluca]

PR #296 provides at least a starting point for this. Needs to be tested better before closing this issue.