Add documentation site

[marctc]

• Added initial structure to render docs with github pages. We decided to use hugo as is the tool used for Prometheus' client_java (see docs here). It's also quite popular tool among open source projects.
• README file is being cleaned up to have minimal information. The content is moved to different subsections. I mostly followed the existing hierarchy but I also moved things a bit around. Please take a look and feel free to suggest how to structure it.
• Added github action to deploy changes when master is built. This probably needs to enable the github page in project settings (@fstab can support us on this in case we can't figure how to do it).

In a follow-up PR, I can add Python docstrings of the documented classes. But for the scope of this PR I decided to leave it out.

Fixes #849

This a preview how it renders:

[csmarchbanks]

Just a couple comments, but this looks great!

Is there a good way to deploy this to a github site just to check that CI works before merging? Locally everything looked nice.

[csmarchbanks]

This comment can be removed since we don't have a 1.0.x branch.

[csmarchbanks]

It's probably worth having Labels as a separate item since they are a core part of using this library.

[marctc]

Moved labels and exemplars to their own section. ## Disabling _created metrics is now in the _index.md of instrumenting. I can change if need it.

[marctc]

Is there a good way to deploy this to a github site just to check that CI works before merging?

If I'm not mistaken, the only way to deploy to pages is syncing with a github branch. @fstab did you try to manually deploy the docs? or you just used the github action directly?

[fstab]

I just used the Github action. I didn't even write it, I just copied it out of the Hugo documentation :) https://gohugo.io/hosting-and-deployment/hosting-on-github/

[csmarchbanks]

There were some readme updates that came in with allowing https, would you be willing to rebase this with those new changes?

Otherwise I think this looks good and I can work on any deployment issues in followup PRs if necessary.

[csmarchbanks]

A couple tiny comments, plus the most recent commit needs a DCO signoff.

[csmarchbanks]

Thanks!