Signed-off-by: lish <lish@csdn.net>

A simple implementation of the git.clone command for the configured
instances.
It also includes a credential provider that can clone the repository
without user input using the access token

See merge request gitlab-org/gitlab-vscode-extension!172

Relates to #222

Fix a broken link which direct to CONTRIBUTORS.md

Misc fix in the README.md file

Signed-off-by: NMassimeddu Cireddu <massimeddu@gmail.com>

- Update **Step 2** sub steps with more information
- Reword the "should" to "must" in the instanceUrl description to make clear, that this must be set for custom domains.

closes #88