Allow users to add a link to their snippet repo in the readme

[benmarwick]

@daattali has done a tremendous service to RStudio users with his addinslist package, and multiplied the usefulness further by hosting a list that users can add their add-ins to.

This snippr package seems to be an analogous method for working with snippets, so I wonder what you might think about hosting a similar table of user snippets in the readme for this package?

Then we can invite people to add their snippets to the table, making it easier for others to discover and share, in the same way @daattali does for the add-ins (and maybe get a few more people using them, I'm keen for all the clever rstats people to share their snippets so I can use them too!)

[daattali]

When I first saw this package I thought "cool, I should share my snippets!" and immediately thought "but that's kind of a lame thing to tweet... and after the initial tweet, it'll be forgotten forever".

So I completely agree :)

[gadenbuie]

I know I'm a ~~little~~ few years late to the party, but in lieu of a central list of snippets here's a GitHub search that looks for r.snippets files in the base folder of repos on GitHub: https://github.com/search?q=in%3Apath+r.snippets+type%3Acode&type=Code