add netlify deploy badge

[javorszky]

Because this site is for a noncommercial events thing, we can get an open source netlify team included, so I could invite y'all as team members into the netlify deployment settings thingy.

In order to do that, the project needs to adhere to their open source policies as outlined here: https://www.netlify.com/legal/open-source-policy/

To qualify for the Open Source plan, a project must adhere to the following criteria:

• Includes a license listed on the Open Source Initiative approved license list or a Creative Commons license that includes “attribution” or places the work in the public domain. (ISC License is on the list of approved ones)
• Features a Code of Conduct at the top level directory of the project repository or prominently in the documentation (with a link in the navigation, footer, or homepage). (see added code of conduct #6)
• Must feature a link to our service on your main page, or all internal pages. You have two options:
  - We have premade badges for your convenience, or (this is this PR, I chose the black one)
  - You may create your own link, which should read “This site is powered by Netlify”, and include a link back to our home page.
• Must not be a commercial project, whether created by a company or an individual. This prohibition includes commercial support and hosting services. (yep, not a commercial project)

There are a bunch more styles (see the premade badges link), or, as stated, we can create our own link.

[omgmog]

I think let's wait until #8 is in, and then have a think about tidying up the footer because the symmetry of it will be lost after this and the code of conduct links are integrated.

[javorszky]

This has been rebased over current main after merging in #8