Add link to subcommands

[saroad2]

Description

When documenting a group or multicommand using mkdocs-click, added a new section elaborating the subcommands with links to full documentation:

This new ability can be disabled using list_subcommands to False. True by default

[saroad2]

Hey @ofek ,

Done :) Thanks for the feedback!

[saroad2]

@ofek , Would you mind creating a new release so I could use that ability in my project?

[ofek]

https://github.com/DataDog/mkdocs-click/releases/tag/0.8.0

[saroad2]

Thanks!