update LICENSE and COC links

[zkamvar]

Since the user is always directed here, the links should point to the correct pages. The COC link is a bit bare, however since the relevant content is Jekyll-derived. Maybe we should just link the Carpentries code of conduct instead?

[maneesha]

This came up in another context before, where GitHub automatically links to a project's COC file. I agree that this should link to our CoC.

[maxim-belkin]

Thank you for the PR, Zhian.
Thank you for your comment, Maneesha.

When maintainers synchronize lessons with carpentries/styles repository, they copy files from bin/boilerplate directory to the corresponding lessons' directories. So, bin/boilerplate/CONTRIBUTING.md is copied to the root folder replacing the current CONTRIBUTING.md file. The change suggested in this PR would, therefore, brake the link.

We can link to https://docs.carpentries.org/topic_folders/policies/index_coc.html, however, I feel that we should discuss this change before implementing it