Collecting some agency practices

This is a tiny pull request, just kicking off a `practices.md` document to collect interesting things from around the government. 

I started it off with some links and description of the CFPB and State -- but @jackiekazil @rjmajma @vz3 I know we've collected a lot more notes than this, so please update `practices.md` with more work. No need to submit future PRs for it, just edit it like you would the wiki. This PR is just to put a little flag in the sand.