MISC: Improve tutorial, documentation and discoverability of NS API documentation

[catloversg]

Tutorial

• Change the example of the hack script:
  • Add /** @param {NS} ns */.
  • Change the tab character to double space characters.
• Mention "NS API documentation".

Documentation

Update README.md.

Discoverability of NS API documentation:

Script Editor tab:
Before:

After:

Documentation tab:
Before:

After:

Note: There is a "side-effect" of this change: all external links will be changed in the same way as the NS API documentation link. For example:

Closes #1696.

[d0sboots]

I think the "side-effect" of external links being styled a little differently is a good one. It shouldn't be a style difference for just the NS API, it is better for it to be a systematic reason.