how to edit on github

We have an Edit on Github link, but if you aren't sure how to use it, it probably doesn't help that much.

So we need:

- clear instructions on the process (probably a small document linked from docs-tech)
- clear guidelines about what sorts of edits are reasonable to do without a local setup

Start by inspecting the current Edit on Github link and the docs-tech documentation area. Add a short explanation of the editing process and guidelines for edits that can be made without a local setup; the work is done when both topics are clearly documented and linked from the relevant documentation.

Written by the indexing model from the issue text.