I have a project hosted on GitHub. For this I have written my README using the Markdown syntax in order to have it nicely formatted on GitHub.
As my project is in Py
I would recommend Pandoc, the "swiss-army knife for converting files from one markup format into another" (check out the diagram of supported conversions at the bottom of the page, it is quite impressive). Pandoc allows markdown to reStructuredText translation directly. There is also an online editor here which lets you try it out, so you could simply use the online editor to convert your README files.