Mimic GitHub readme format for parameters table

[jwparsons]

Here's an example:

Render a snippet

https://digist.azurewebsites.net/gist/{gist_id}?file={file}&slice={slice}&theme={theme}

Name	Description
gist_id	Gist ID from GitHub
file	The default file shown by the snippet
slice	The lines of file shown by the snippet, formatted as {startLine}:{endLine}
theme	Optional: either dark (default) or light

Originally posted by @jungaretti in #63 (comment)