Add Intro lectures to Projects page

[DrDrij]

This PR adds a link and title square on the Project page (https://quantecon.org/projects/#filter=lecture) for Computational Economics and Finance for Undergraduates (https://intro.quantecon.org/).

@jstac This is parked until you green light.

[jstac]

Thanks @DrDrij . Title has changed --- see https://intro.quantecon.org/intro.html

[mmcky]

@DrDrij I have updated the title in the md file

[mmcky]

It looks like #107 supersedes this PR

[HengchengZhang]

Closed as #107