add new reporters section in the readme

[arings]

Fixes / updates #898

[nfcampos]

that screenshot is for npm's verbose mode not ava´s. you'd have to run npm test -- --verbose to get ava's verbose mode, without the extra -- you're passing the verbose flag to npm itself

[arings]

I am very sorry for that. AVA is new to me, and I am new to new technologies. As I understand correctly - old screenshot was sufficient, so I put it instead.

[nfcampos]

No need to apologise :) passing flags to npm run is rather confusing

[sindresorhus]

Tap reporter

[sindresorhus]

Also need to update the link in "Why AVA?" then.

[jamestalmage]

All caps (TAP) is the preferred representation based on the website http://testanything.org

[arings]

'Optional TAP output' >> 'TAP reporter',
links in 'Why AVA?' updated,
Mini-reporter mentioned that it's the default reporter,
Verbose reporter mentioned that it can be selected with the --verbose flag,
Reporters section added to the Table of Contents.

[sindresorhus]

Looks good. Thank you @mk-61 :)