Add the master branch buildstats history to the readme.
Add the master branch buildstats history to the readme.

Note: Currently, darga history doesn't currently appear to work properly, but it
would look something like this:

`[![Build history for darga branch](https://buildstats.info/travisci/chart/ManageIQ/manageiq?branch=darga)](https://travis-ci.org/ManageIQ/manageiq/branches)`

[ci skip]

mfeifer/manageiq,aufi/manageiq,jrafanie/manageiq,romanblanco/manageiq,mzazrivec/manageiq,pkomanek/manageiq,maas-ufcg/manageiq,billfitzgerald0120/manageiq,durandom/manageiq,d-m-u/manageiq,israel-hdez/manageiq,jntullo/manageiq,aufi/manageiq,agrare/manageiq,skateman/manageiq,yaacov/manageiq,mkanoor/manageiq,tinaafitz/manageiq,juliancheal/manageiq,aufi/manageiq,chessbyte/manageiq,israel-hdez/manageiq,romanblanco/manageiq,NaNi-Z/manageiq,jvlcek/manageiq,kbrock/manageiq,matobet/manageiq,maas-ufcg/manageiq,tzumainn/manageiq,kbrock/manageiq,ailisp/manageiq,ilackarms/manageiq,d-m-u/manageiq,josejulio/manageiq,jntullo/manageiq,jameswnl/manageiq,mkanoor/manageiq,djberg96/manageiq,billfitzgerald0120/manageiq,kbrock/manageiq,tinaafitz/manageiq,chessbyte/manageiq,josejulio/manageiq,mresti/manageiq,maas-ufcg/manageiq,ManageIQ/manageiq,skateman/manageiq,agrare/manageiq,matobet/manageiq,mfeifer/manageiq,NaNi-Z/manageiq,matobet/manageiq,andyvesel/manageiq,matobet/manageiq,durandom/manageiq,hstastna/manageiq,KevinLoiseau/manageiq,hstastna/manageiq,pkomanek/manageiq,jrafanie/manageiq,yaacov/manageiq,fbladilo/manageiq,ilackarms/manageiq,d-m-u/manageiq,billfitzgerald0120/manageiq,ManageIQ/manageiq,ailisp/manageiq,skateman/manageiq,KevinLoiseau/manageiq,mfeifer/manageiq,fbladilo/manageiq,gmcculloug/manageiq,syncrou/manageiq,pkomanek/manageiq,romaintb/manageiq,mzazrivec/manageiq,pkomanek/manageiq,maas-ufcg/manageiq,NickLaMuro/manageiq,durandom/manageiq,ilackarms/manageiq,josejulio/manageiq,romanblanco/manageiq,mzazrivec/manageiq,juliancheal/manageiq,branic/manageiq,jvlcek/manageiq,KevinLoiseau/manageiq,andyvesel/manageiq,hstastna/manageiq,billfitzgerald0120/manageiq,gmcculloug/manageiq,romaintb/manageiq,romaintb/manageiq,borod108/manageiq,maas-ufcg/manageiq,jvlcek/manageiq,fbladilo/manageiq,lpichler/manageiq,ailisp/manageiq,maas-ufcg/manageiq,branic/manageiq,gerikis/manageiq,mfeifer/manageiq,romanblanco/manageiq,jameswnl/manageiq,NaNi-Z/manageiq,gmcculloug/manageiq,chessbyte/manageiq,mresti/manageiq,agrare/manageiq,tzumainn/manageiq,mkanoor/manageiq,KevinLoiseau/manageiq,gerikis/manageiq,israel-hdez/manageiq,skateman/manageiq,ailisp/manageiq,mresti/manageiq,mresti/manageiq,hstastna/manageiq,tinaafitz/manageiq,d-m-u/manageiq,jntullo/manageiq,ManageIQ/manageiq,djberg96/manageiq,borod108/manageiq,chessbyte/manageiq,fbladilo/manageiq,syncrou/manageiq,agrare/manageiq,syncrou/manageiq,jameswnl/manageiq,djberg96/manageiq,juliancheal/manageiq,ManageIQ/manageiq,israel-hdez/manageiq,jvlcek/manageiq,borod108/manageiq,mzazrivec/manageiq,aufi/manageiq,NickLaMuro/manageiq,gerikis/manageiq,jrafanie/manageiq,romaintb/manageiq,NickLaMuro/manageiq,branic/manageiq,tzumainn/manageiq,NaNi-Z/manageiq,josejulio/manageiq,yaacov/manageiq,lpichler/manageiq,yaacov/manageiq,syncrou/manageiq,andyvesel/manageiq,KevinLoiseau/manageiq,kbrock/manageiq,gmcculloug/manageiq,romaintb/manageiq,borod108/manageiq,branic/manageiq,andyvesel/manageiq,jntullo/manageiq,durandom/manageiq,tinaafitz/manageiq,romaintb/manageiq,gerikis/manageiq,ilackarms/manageiq,KevinLoiseau/manageiq,jrafanie/manageiq,mkanoor/manageiq,lpichler/manageiq,djberg96/manageiq,lpichler/manageiq,jameswnl/manageiq,NickLaMuro/manageiq,tzumainn/manageiq,juliancheal/manageiq