Include Code of Conduct in GitHub-recognised manner. (#25751)
Include Code of Conduct in GitHub-recognised manner. (#25751)

This is just a link to the code of conduct at
http://www.dotnetfoundation.org/code-of-conduct which is already linked
to in the readme.

Putting it at this location just has github recognise it as such
(https://github.com/dotnet/corefx/community)

The text is the same as that used at
https://github.com/dotnet/docs/blob/master/CODE_OF_CONDUCT.md
Ermiar/corefx,zhenlan/corefx,ptoonen/corefx,ericstj/corefx,Jiayili1/corefx,shimingsg/corefx,shimingsg/corefx,ericstj/corefx,Jiayili1/corefx,Jiayili1/corefx,Ermiar/corefx,zhenlan/corefx,shimingsg/corefx,wtgodbe/corefx,Ermiar/corefx,ViktorHofer/corefx,ViktorHofer/corefx,ravimeda/corefx,Ermiar/corefx,ptoonen/corefx,wtgodbe/corefx,ericstj/corefx,BrennanConroy/corefx,axelheer/corefx,ericstj/corefx,axelheer/corefx,zhenlan/corefx,ViktorHofer/corefx,ptoonen/corefx,Jiayili1/corefx,ravimeda/corefx,ravimeda/corefx,axelheer/corefx,ViktorHofer/corefx,mmitche/corefx,ptoonen/corefx,zhenlan/corefx,mmitche/corefx,axelheer/corefx,zhenlan/corefx,Jiayili1/corefx,shimingsg/corefx,BrennanConroy/corefx,mmitche/corefx,mmitche/corefx,axelheer/corefx,ptoonen/corefx,ericstj/corefx,ravimeda/corefx,mmitche/corefx,wtgodbe/corefx,ptoonen/corefx,mmitche/corefx,wtgodbe/corefx,ravimeda/corefx,BrennanConroy/corefx,Jiayili1/corefx,axelheer/corefx,ericstj/corefx,ericstj/corefx,Jiayili1/corefx,Ermiar/corefx,ravimeda/corefx,mmitche/corefx,ptoonen/corefx,ravimeda/corefx,shimingsg/corefx,shimingsg/corefx,wtgodbe/corefx,zhenlan/corefx,zhenlan/corefx,Ermiar/corefx,wtgodbe/corefx,ViktorHofer/corefx,wtgodbe/corefx,shimingsg/corefx,ViktorHofer/corefx,Ermiar/corefx,ViktorHofer/corefx