PARQUET-57 - Update dev README to clarify two points

Author: Brock Noland <brock@apache.org>

Closes #26 from brockn/PARQUET-57 and squashes the following commits:

ffb2a9a [Brock Noland] Prompt for jira user/pass if not set
0135cdd [Brock Noland] Fix spelling
171d714 [Brock Noland] PARQUET-57 - Update dev README to clarify two points