adding coustomer groups documentation
modified discount_rules example to be correct json
moved to right place
added create, update and delete info to customer addresses endpoint and tweaked the groups doc
Added documentations for orders post
Merge pull request #12 from mechatama/orders-post

Added documentations for orders post
Merge pull request #11 from chaitanyakuber/master

Documentation for Customer Groups & Addresses
Fixed up some small typos
Merge pull request #13 from troycox/patch-2

Fixed up some small typos