Update data sources page to include ion channels info

[slarson]

The data sources page should get updated along with the new ion channel content. The source is here. It should be easy to follow the pattern that is already laid out, including linking to the relevant spreadsheet, the TSV file in Github, and pointing to the relevant code line in insert_worm.py

[shubhsingh594]

the names and data about the ion channels have been taken from the channelworm django app, what should I cite as the source for this, as there is no spreadsheet.