Using GET makes tries bookmarkable and easier to share.

I want to use try.docopt.org in an online discussion about a CLI.

This makes examples easier to share.

And using POST was unnecessary:
   - there's no server state, so requests are always *safe*
   - every request with the same `doc` and `argv` should render the same response (unless after the event of a major docopt update), which makes them *idempotent*.

GET fits nicely.