Add a hint on the install guide to disable C extensions with pip.
Add a hint on the install guide to disable C extensions with pip.

ThiefMaster/sqlalchemy,brianv0/sqlalchemy,pdufour/sqlalchemy,Cito/sqlalchemy,WinterNis/sqlalchemy,WinterNis/sqlalchemy,davidjb/sqlalchemy,276361270/sqlalchemy,sandan/sqlalchemy,monetate/sqlalchemy,hsum/sqlalchemy,Akrog/sqlalchemy,alex/sqlalchemy,sqlalchemy/sqlalchemy,EvaSDK/sqlalchemy,robin900/sqlalchemy,ThiefMaster/sqlalchemy,graingert/sqlalchemy,olemis/sqlalchemy,monetate/sqlalchemy,wfxiang08/sqlalchemy,hsum/sqlalchemy,bdupharm/sqlalchemy,bootandy/sqlalchemy,wujuguang/sqlalchemy,halfcrazy/sqlalchemy,alex/sqlalchemy,davidfraser/sqlalchemy,inspirehep/sqlalchemy,Cito/sqlalchemy,olemis/sqlalchemy,bootandy/sqlalchemy,epa/sqlalchemy,j5int/sqlalchemy,EvaSDK/sqlalchemy,brianv0/sqlalchemy,robin900/sqlalchemy,inspirehep/sqlalchemy,pdufour/sqlalchemy,wujuguang/sqlalchemy,zzzeek/sqlalchemy,sandan/sqlalchemy,elelianghh/sqlalchemy,bdupharm/sqlalchemy,Cito/sqlalchemy,elelianghh/sqlalchemy,epa/sqlalchemy,graingert/sqlalchemy,276361270/sqlalchemy,wfxiang08/sqlalchemy,Akrog/sqlalchemy,dstufft/sqlalchemy,davidjb/sqlalchemy,itkovian/sqlalchemy,alex/sqlalchemy,j5int/sqlalchemy,davidfraser/sqlalchemy,dstufft/sqlalchemy,halfcrazy/sqlalchemy,itkovian/sqlalchemy