#112: Add documentation

[maxime-bfsquall]

Fixes #112

[maxime-bfsquall]

Waiting for a way to "commit" and "push" the generated documentation on DARMA-tasking.github.io repository using another method.

Current method based on VT : Defining a user (name/email) and using a token passed by the variable secrets.GH_PAT to the CI

[maxime-bfsquall]

Before the merge, we have to change the documentation GIT branch used for tests 112-add-documentation to master

[cwschilly]

I added the README from PR #59 into mainpage.md -- once that PR is approved I'll update this one with any more small changes

[tlamonthezie]

Before the merge, we have to change the documentation GIT branch used for tests 112-add-documentation to master

Hello @maxime-bfsquall I think you can do these changes now is has been already been approved