the GitHub wiki is a great source of documentation, unfortunately it seems like only the members with write access can update it. IIUC the GitHub solution is to use a dedicated project for the wiki content, e.g. dhall-lang/dhall-wiki with automation to sync the content to the dhall-lang.wiki.git. Another solution would be to move the wiki page into regular markdown file.
Could the wiki accept contribution through pull-request?
For example, I would like to propose a change to replace the unicode symbol with their ascii version, and perhaps suggest a new ‘Examples’ page with some practical content to help get started.