Update README.md
updated example in PHP

added config and index(for submit form), update checkorder,
paymentaviso.
Update README.md
Merge pull request #3 from YandexMoney/master

Merge pull request #3 from aTastyCookie/master
Update README.md
update russian MWS to 3.1
Merge pull request #4 from aTastyCookie/master

pull request