Increase timeout in ID mapping script

[keithchev]

This PR attempts to address #94 by increasing the timeout in the map_refseq_ids.py script. As far as I can tell, the UniProt mapping API is unchanged but may have become slower, resulting in the script failing if the mapping job takes longer than the previous timeout (of 300 seconds).

This PR increases the timeout to 3000 seconds.

Anecdotally, the mapping requests for the two default databases ("EMBL-GenBank-DDBJ_CDS" and "RefSeq_Protein") are currently taking around 800 seconds and 150 seconds, respectively.

Driveby changes

• Minor cleanup and variable renaming in map_refseq_ids.py for clarity.
• Improve README formatting.

Testing

I tested the map_refseq_ids.py script manually and ran the tests locally. The CI is currently broken.

PR checklist

• Tag the issue(s) or milestones this PR fixes (e.g. Fixes #123, Resolves #456).
• Describe the changes you've made.
• Describe any tests you have conducted to confirm that your changes behave as expected.