Manual override of citation dates with sources.yaml

Firstly, **_thank you_** for creating this lab website template, it's been really great.

I had a bit of trouble with the publication dates for the research page – they were not automatically being parsed by Manubot (I think), and then when I followed the documentation for the manual override in sources.yaml, it was leaving the [no date info] in place on the website.

I found the solution was to report the date within in single quotes,`date: 'YYYY-MM-DD'` -- rather than `date: YYYY-MM-DD` as suggested by the documentation and in the provided example.

Additional note - In the main lab-website-template repo, the first item in the `sources.yaml` file has the date written is as `date: 2020-12-4`, which I think somehow gets updated to the correct date format by `citation.html`.

Start with the documentation for manually overriding citation dates and the provided sources.yaml example. Update the example and wording to show the date in single quotes, then verify that the documented format prevents the [no date info] text from remaining on the website.

Written by the indexing model from the issue text.