README feedback items

[pearsonca]

Generally good README. Some notes, mostly concerning the README directly, but some with knock-on edits.

• Data First link seems to be improperly formatted. Linking to that top level page seems insufficient guidance for asking about data access.
• would be nice to have a link to description of data set itself (e.g., any publications? page on Data First devoted to this data set?)
• "Setup Instructions" directions mildly imply that python 3 would be installed as part of cloning process.
• directions say "Navigate to...dlr_data_retrieval", but the structure picture says "dlr_data"
• for update cnxtnstr.txt, link to file itself in repository? Possible to make filling in that file easier? E.g. Server={REPLACE EVERYTHING WITHIN BRACES BY XX.YY.ZZ};
• for start & end years: exclusive or inclusive?
• command line convention: - should be used with single, lowercase letters. So recommend -c instead of -csv. The latter is read as combining the c, s, and v flags. Should be able to specify a long form option as --csv.