Add automatic documentation deployment workflow

[king-p3nguin]

Resolve #385

The automatically deployed documentation is available at: https://king-p3nguin.github.io/Tangelo/

Settings for GitHub Pages is as follows:

(I am contributing to this project as a unitaryHACK participant)

[ValentinS4t1qbit]

@king-p3nguin Sorry for my ignorance: I forget whether the repo maintainers should create a gh-pages branch in order to follow your instructions and if yes, can I just create it from any other branch ? (e.g does it matter how it was created ?)

Sorry, Github's documentation on the matter is sending me on a journey through a number of pages without answering my question

[king-p3nguin]

@ValentinS4t1qbit When I tried running this workflow on my fork, peaceiris/actions-gh-pages@v4 automatically created gh-pages branch, so I think maintainers do not need to create this branch manually.

[ValentinS4t1qbit]

@ValentinS4t1qbit When I tried running this workflow on my fork, peaceiris/actions-gh-pages@v4 automatically created gh-pages branch, so I think maintainers do not need to create this branch manually.

@king-p3nguin I cannot select it like in your screenshot, the drop-down menu only offer existing branches. Maybe a better question is: why wouldn't we select main ? (I do not quite recall why the issue description stated gh-pages, maybe we did not quite get how to do this right).

[king-p3nguin]

@ValentinS4t1qbit
This workflow is not executed until the yaml file is pushed to the main branch, so the gh-pages branch has not been created yet. It should be created through the workflow as soon as this PR is merged.

I think the reason peaceiris/actions-gh-pages@v4 pushes documentation to the separate gh-pages branch instead of the main branch is to simplify the commit history. (If it is pushed to main, than the commit history of main branch will be like "PR merge commit -> new document push ->PR merge commit -> new document push ->")

[ValentinS4t1qbit]

@king-p3nguin Alright, I'll give it a shot. The finish line for the hack is closing the issue, it is ok it we somehow need two separate PRs for adjustments.