Generating an about.md

[NJichev]

We could generate a summary of all the posts/pages. I have these features in mind:

• It should be customizable(i.e. specifying only these folders, adding some more templates and stuff, like tags).
• We should be able to add our own content to the generated thing(example: social links or homework tasks).
• Pass in links to the other pages?

This will be useful when you create new lectures, which will be automatically added to this list.