doc: replace URL action example with form The example to provide a link to take or resolve an item was broken. Roundup has required a POST not GET for changes to the database for a while. This example was never fixed. Replaced a link using GET with a POSTed form. This changes the activating element from a link to a button. The button could be restyled as a link using CSS I think. The original example was also not canonical. It used :action rather than the canonical @action.

#!/usr/bin/env python
from __future__ import print_function
import zlib, base64, sys
print(base64.encodestring(zlib.compress(sys.stdin.read())))