Add vertex cover doc. Addresses #701
Add vertex cover doc.
Addresses #701

jni/networkx,bzero/networkx,dmoliveira/networkx,farhaanbukhsh/networkx,jni/networkx,kernc/networkx,nathania/networkx,jtorrents/networkx,harlowja/networkx,jakevdp/networkx,JamesClough/networkx,sharifulgeo/networkx,dmoliveira/networkx,wasade/networkx,dmoliveira/networkx,NvanAdrichem/networkx,andnovar/networkx,debsankha/networkx,harlowja/networkx,jakevdp/networkx,kai5263499/networkx,nathania/networkx,bzero/networkx,yashu-seth/networkx,harlowja/networkx,jcurbelo/networkx,nathania/networkx,kernc/networkx,RMKD/networkx,jni/networkx,dhimmel/networkx,kernc/networkx,kai5263499/networkx,blublud/networkx,cmtm/networkx,kai5263499/networkx,farhaanbukhsh/networkx,ghdk/networkx,ghdk/networkx,chrisnatali/networkx,goulu/networkx,ionanrozenfeld/networkx,OrkoHunter/networkx,jfinkels/networkx,farhaanbukhsh/networkx,jakevdp/networkx,michaelpacer/networkx,bzero/networkx,RMKD/networkx,dhimmel/networkx,debsankha/networkx,chrisnatali/networkx,sharifulgeo/networkx,sharifulgeo/networkx,tmilicic/networkx,chrisnatali/networkx,ionanrozenfeld/networkx,blublud/networkx,aureooms/networkx,Sixshaman/networkx,debsankha/networkx,RMKD/networkx,jtorrents/networkx,dhimmel/networkx,ionanrozenfeld/networkx,blublud/networkx,SanketDG/networkx,aureooms/networkx,aureooms/networkx,ltiao/networkx,beni55/networkx,ghdk/networkx