update futures README
update futures README

Summary:It's been awhile.

Still has intern URLs (#10943549) but I'll fix that separately.

Reviewed By: jsedgwick

Differential Revision: D3213245

fb-gh-sync-id: ff60193ff368deaac8ca233d4289f30d8f6bb223
fbshipit-source-id: ff60193ff368deaac8ca233d4289f30d8f6bb223

mqeizi/folly,brunomorishita/folly,mqeizi/folly,rklabs/folly,charsyam/folly,rklabs/folly,brunomorishita/folly,rklabs/folly,brunomorishita/folly,Orvid/folly,facebook/folly,brunomorishita/folly,mqeizi/folly,floxard/folly,brunomorishita/folly,rklabs/folly,facebook/folly,charsyam/folly,facebook/folly,floxard/folly,rklabs/folly,facebook/folly,floxard/folly,floxard/folly,mqeizi/folly,charsyam/folly,floxard/folly,charsyam/folly,Orvid/folly,Orvid/folly,mqeizi/folly,facebook/folly,Orvid/folly,Orvid/folly