[Request] Changes to the Readme.md

[toby63]

Additions:

• mention that we would like to see translations (right now this is not mentioned)
  • and maybe a status of translations and participants (if possible)
• Writing Guidelines:
  • mostly Markdown with a bit of html
  • I could add some specifics I included, such as special css-classes for notes etc.
  • different "styles" for website versus documentation
• link directly to open issues, for example: Issue about the Advanced Guide
• mention Ideas and Feature Requests (and not just "Bug Reports")

Corrections:

• python3-markdown (<3.0.0), is not <3.0.0 anymore

Comment:
I can work on Pull requests for most of this, but I wanted to hear oppinions first 😄.

[toby63]

@stgraber What is your oppinion on sparse-checkouts?

I am thinking about adding it to the git clone instructions in README.md, because the Downloads-folder is quite big and unnecessary for people who want to edit the website.

[stgraber]

Yeah, that should be fine. Unless they're working on the rendering of the download pages that is.

[toby63]

Added with #463 and #464.