Added clarification to README
Added clarification to README

Signed-off-by: Nick Quaranto <75ef9faee755c70589550b513ad881e5a603182c@quaran.to>

thewatts/shoulda-matchers,alejandrogutierrez/shoulda-matchers,reacuna/shoulda-matchers,taichiman/shoulda-matchers,raysrashmi/shoulda-matchers,bmaddy/shoulda,NafaaBout/shoulda-matchers,maurogeorge/shoulda-matchers,plribeiro3000/shoulda-matchers,awmichel/shoulda-matchers,reacuna/shoulda-matchers,guialbuk/shoulda-matchers,plribeiro3000/shoulda-matchers,stanchan/shoulda-matchers,awmichel/shoulda-matchers,maurogeorge/shoulda-matchers,thoughtbot/shoulda-matchers,thewatts/shoulda-matchers,timoschilling/shoulda-matchers,taichiman/shoulda-matchers,fxposter/shoulda-matchers,stanchan/shoulda-matchers,guialbuk/shoulda-matchers,cheshire-cat/shoulda-matchers,stanchan/shoulda-matchers,timoschilling/shoulda-matchers,biow0lf/shoulda-matchers,guialbuk/shoulda-matchers,phaza/shoulda,biow0lf/shoulda-matchers,AlexVPopov/shoulda-matchers,raysrashmi/shoulda-matchers,thoughtbot/shoulda-matchers,alejandrogutierrez/shoulda-matchers,plribeiro3000/shoulda-matchers,raysrashmi/shoulda-matchers,timoschilling/shoulda-matchers,cheshire-cat/shoulda-matchers,reacuna/shoulda-matchers,biow0lf/shoulda-matchers,alejandrogutierrez/shoulda-matchers,PikachuEXE/shoulda-matchers,biow0lf/shoulda-matchers,AlexVPopov/shoulda-matchers,thoughtbot/shoulda,cheshire-cat/shoulda-matchers,plribeiro3000/shoulda-matchers,raysrashmi/shoulda-matchers,thoughtbot/shoulda-context,maurogeorge/shoulda-matchers,NafaaBout/shoulda-matchers,NafaaBout/shoulda-matchers,NafaaBout/shoulda-matchers,AlexVPopov/shoulda-matchers,stanchan/shoulda-matchers,thewatts/shoulda-matchers,thoughtbot/shoulda-context,ratnikov/shoulda,timoschilling/shoulda-matchers,awmichel/shoulda-matchers,AlexVPopov/shoulda-matchers,taichiman/shoulda-matchers,thoughtbot/shoulda,guialbuk/shoulda-matchers,cheshire-cat/shoulda-matchers,alejandrogutierrez/shoulda-matchers,awmichel/shoulda-matchers,reacuna/shoulda-matchers,thewatts/shoulda-matchers,taichiman/shoulda-matchers,thoughtbot/shoulda-matchers,thoughtbot/shoulda-matchers,smeder/shoulda