Contributors table in markdown

**Is your feature request related to a problem? Please describe.**

_Highly likely this design was discussed and a decision was taken to use html but I could not find any references._

The contributors table in html markup is not displayed as table when parsed through libraries that expect only markdowns. HTML tags are stripped/escaped or ignored by default by react markdown renderers for example which causes the contributors table to be displayed as code or not displayed.

**Describe the solution you'd like**

An option to generate the table in markdown syntax.

**Describe alternatives you've considered**

Using a separate "staging" file for all-contributors bot and add a post processing step to convert to markdown and add to readme.

**Additional context**
This feature is for use cases where the readme or contributors files are displayed in non-github browser UIs which do not expect or encourage html