Add more descriptions for tags and categories

[gouravkhunger]

Descriptions on tags and categories are stored in _data/descriptions.yml file.

They are rendered on archive pages, example.

These are the existing tags and categories.

Adding new descriptions is easy. For example, adding description for tag open-source is as easy as adding:

open-source: "Description"

And it will render on all archive pages for open-source (either tag/category).

We need to add more descriptions for the existing topics!