Update README for GitLab deployment

[VincentTam]

In the "Prerequisites" section of the README, it's written that a GitHub account is required. Nonetheless, it turned out that this theme also works on GitLab, with an addition of an appropriate GitLab CI config file and the line exclude: vendor in _config.yml. For a proof of this, you may see my demo GitLab repo and the associated Beautiful Jekyll + Framagit demo site created for testing this theme's reCAPTCHA support in einsteinpy/blog.einsteinpy.org#356.

Reference: https://www.chenhuijing.com/blog/hosting-static-site-gitlab-pages/

[daattali]

@VincentTam if what you said is still true for GitLab, I'd be happy to accept a small PR to the README

[iootaa]

A free and open-source instance of Gitlab allows to use Jekyll. The host is french and so the doc is : https://framablog.org/2017/03/20/les-gitlab-pages-debarquent-dans-framagit/

[daattali]

@iootaa Feel free to add a few sentences to the README on how to translate this into GitLab!

[VincentTam]

@iootaa Thx for info. I tested that a year ago on Framagit, the free (as in freedom) GitLab instance that you've mentioned: https://framagit.org/staticman-gitlab-pages, and I would say that it works with almost any static web generator you can think of, thanks to the built-in GitLab CD/CI, which can execute any Docker image (hosted on either Docker Hub or GitLab container registry).

However, as Staticman's project maintainer no longer suggests using public (or shared) API instance in eduardoboucas/staticman#317 (comment), I removed the links between the Git* bots and my API instances on Heroku. I'm going to start a new issue about this and update this repo's README.

[VincentTam]

Closing due to removal of technical instructions about comment service integration in the README.