Add reward videos to bot topics

[lizTheDeveloper]

Add reward videos to each topic. These videos should be interesting, and curiosity-invoking.

Start with:

• JavaScript: source from JSConf, Google.io, other JS conferences, D3.js conf, etc
• Python: source from PyCon, also popular python packages like pandas
• Comp Sci: source from ComputerPhile
• SQL: look for SQL tricks, try to find database-agnostic tricks

Add them under the Topic's readme file (we may move these later, be ready to write a migration script)

reward_videos:
  - '[enki link format](http://youtu.be/whatever){video}'