doc: add note on how to skip tests when building from source
doc: add note on how to skip tests when building from source

closes #460

davecramer/pgjdbc,zapov/pgjdbc,AlexElin/pgjdbc,jamesthomp/pgjdbc,jorsol/pgjdbc,davecramer/pgjdbc,zemian/pgjdbc,AlexElin/pgjdbc,marschall/pgjdbc,Gordiychuk/pgjdbc,jamesthomp/pgjdbc,golovnin/pgjdbc,davecramer/pgjdbc,zapov/pgjdbc,panchenko/pgjdbc,panchenko/pgjdbc,zemian/pgjdbc,AlexElin/pgjdbc,zemian/pgjdbc,whitingjr/pgjdbc,zapov/pgjdbc,marschall/pgjdbc,jorsol/pgjdbc,marschall/pgjdbc,davecramer/pgjdbc,Gordiychuk/pgjdbc,sehrope/pgjdbc,jkutner/pgjdbc,jorsol/pgjdbc,jamesthomp/pgjdbc,lordnelson/pgjdbc,sehrope/pgjdbc,panchenko/pgjdbc,lordnelson/pgjdbc,lordnelson/pgjdbc,jkutner/pgjdbc,golovnin/pgjdbc,jorsol/pgjdbc,Gordiychuk/pgjdbc,marschall/pgjdbc,pgjdbc/pgjdbc,golovnin/pgjdbc,pgjdbc/pgjdbc,pgjdbc/pgjdbc,whitingjr/pgjdbc,sehrope/pgjdbc,pgjdbc/pgjdbc,sehrope/pgjdbc,whitingjr/pgjdbc,jkutner/pgjdbc