Update Contributing.md [skip ci]
Update Contributing.md [skip ci]

* Update Contributing.md

After reading this I realized it was a bit dated.
I've also attempted to massage the grammar.

marschall/pgjdbc,AlexElin/pgjdbc,davecramer/pgjdbc,jorsol/pgjdbc,golovnin/pgjdbc,golovnin/pgjdbc,marschall/pgjdbc,sehrope/pgjdbc,sehrope/pgjdbc,jorsol/pgjdbc,jorsol/pgjdbc,marschall/pgjdbc,sehrope/pgjdbc,pgjdbc/pgjdbc,AlexElin/pgjdbc,pgjdbc/pgjdbc,pgjdbc/pgjdbc,sehrope/pgjdbc,AlexElin/pgjdbc,golovnin/pgjdbc,pgjdbc/pgjdbc,davecramer/pgjdbc,davecramer/pgjdbc,marschall/pgjdbc,jorsol/pgjdbc,davecramer/pgjdbc