Add ports/URLs to descriptions.

[roerohan]

Update URLs and netcat ports in challenge.ymls and READMEs.

[roerohan]

@thebongy @theProgrammerDavid @AJ1479 @ritwikgoel
I think I've added the challenge links to all of the challenges which need them. Please verify once.
@AJ1479 @ritwikgoel , just check that all the challenges which have a nodePort specified in challenge.yml have a link (in case of web), or a netcat string in the description.

[roerohan]

This is probably done everywhere. Closing for now, might reopen if needed.
@thebongy