Cider nREPL configuration updated in README

[danielsz]

Hi,

As discussed in #115, an updated configuration example for Cider nREPL, and a couple of typo fixes.

[bbatsov]

The proposed changes look good to me, although users might still have to add some middleware by themselves and then using the handler won't work. Probably it's better to show generic examples instead of editor-specific examples.