[doc] Document WatchKit and extension support
[doc] Document WatchKit and extension support

Summary: WatchKit support is now feature complete; document how to use it.

Test Plan: ```./docs/soyweb-local.sh```

grumpyjames/buck,dsyang/buck,Addepar/buck,bocon13/buck,bocon13/buck,zpao/buck,nguyentruongtho/buck,bocon13/buck,ilya-klyuchnikov/buck,OkBuilds/buck,SeleniumHQ/buck,OkBuilds/buck,JoelMarcey/buck,daedric/buck,clonetwin26/buck,illicitonion/buck,Dominator008/buck,JoelMarcey/buck,Distrotech/buck,JoelMarcey/buck,davido/buck,justinmuller/buck,dsyang/buck,rhencke/buck,dsyang/buck,Dominator008/buck,rhencke/buck,bocon13/buck,romanoid/buck,marcinkwiatkowski/buck,daedric/buck,vschs007/buck,nguyentruongtho/buck,raviagarwal7/buck,marcinkwiatkowski/buck,rowillia/buck,clonetwin26/buck,sdwilsh/buck,rhencke/buck,zpao/buck,shybovycha/buck,Distrotech/buck,mogers/buck,rowillia/buck,SeleniumHQ/buck,liuyang-li/buck,justinmuller/buck,rowillia/buck,tgummerer/buck,mogers/buck,k21/buck,grumpyjames/buck,Distrotech/buck,k21/buck,romanoid/buck,brettwooldridge/buck,kageiit/buck,grumpyjames/buck,mogers/buck,Addepar/buck,clonetwin26/buck,shs96c/buck,marcinkwiatkowski/buck,rmaz/buck,sdwilsh/buck,vine/buck,kageiit/buck,SeleniumHQ/buck,kageiit/buck,janicduplessis/buck,dsyang/buck,k21/buck,raviagarwal7/buck,marcinkwiatkowski/buck,daedric/buck,tgummerer/buck,Distrotech/buck,LegNeato/buck,zpao/buck,mikekap/buck,vine/buck,JoelMarcey/buck,dsyang/buck,nguyentruongtho/buck,vschs007/buck,SeleniumHQ/buck,JoelMarcey/buck,grumpyjames/buck,Dominator008/buck,mikekap/buck,Addepar/buck,Dominator008/buck,mikekap/buck,zhan-xiong/buck,zhan-xiong/buck,shybovycha/buck,JoelMarcey/buck,clonetwin26/buck,SeleniumHQ/buck,shybovycha/buck,mikekap/buck,sdwilsh/buck,tgummerer/buck,romanoid/buck,shs96c/buck,daedric/buck,justinmuller/buck,liuyang-li/buck,Distrotech/buck,mogers/buck,daedric/buck,davido/buck,Distrotech/buck,darkforestzero/buck,darkforestzero/buck,LegNeato/buck,liuyang-li/buck,tgummerer/buck,rhencke/buck,justinmuller/buck,brettwooldridge/buck,illicitonion/buck,facebook/buck,rhencke/buck,janicduplessis/buck,daedric/buck,davido/buck,romanoid/buck,daedric/buck,robbertvanginkel/buck,liuyang-li/buck,vine/buck,daedric/buck,davido/buck,raviagarwal7/buck,illicitonion/buck,k21/buck,shybovycha/buck,zhan-xiong/buck,robbertvanginkel/buck,clonetwin26/buck,shybovycha/buck,brettwooldridge/buck,robbertvanginkel/buck,brettwooldridge/buck,clonetwin26/buck,tgummerer/buck,vschs007/buck,sdwilsh/buck,rmaz/buck,davido/buck,OkBuilds/buck,Dominator008/buck,vschs007/buck,raviagarwal7/buck,Addepar/buck,clonetwin26/buck,ilya-klyuchnikov/buck,raviagarwal7/buck,liuyang-li/buck,LegNeato/buck,Addepar/buck,zpao/buck,vine/buck,Dominator008/buck,ilya-klyuchnikov/buck,romanoid/buck,sdwilsh/buck,k21/buck,raviagarwal7/buck,LegNeato/buck,davido/buck,mogers/buck,liuyang-li/buck,clonetwin26/buck,grumpyjames/buck,marcinkwiatkowski/buck,davido/buck,ilya-klyuchnikov/buck,OkBuilds/buck,bocon13/buck,illicitonion/buck,liuyang-li/buck,OkBuilds/buck,kageiit/buck,shs96c/buck,Addepar/buck,Distrotech/buck,Addepar/buck,rmaz/buck,facebook/buck,OkBuilds/buck,JoelMarcey/buck,vine/buck,rmaz/buck,brettwooldridge/buck,zhan-xiong/buck,facebook/buck,darkforestzero/buck,kageiit/buck,justinmuller/buck,JoelMarcey/buck,illicitonion/buck,brettwooldridge/buck,SeleniumHQ/buck,daedric/buck,LegNeato/buck,shs96c/buck,Addepar/buck,rmaz/buck,nguyentruongtho/buck,darkforestzero/buck,zpao/buck,dsyang/buck,rhencke/buck,mikekap/buck,Addepar/buck,marcinkwiatkowski/buck,liuyang-li/buck,Dominator008/buck,darkforestzero/buck,OkBuilds/buck,sdwilsh/buck,nguyentruongtho/buck,ilya-klyuchnikov/buck,marcinkwiatkowski/buck,LegNeato/buck,illicitonion/buck,illicitonion/buck,Distrotech/buck,grumpyjames/buck,k21/buck,k21/buck,Addepar/buck,sdwilsh/buck,mogers/buck,shs96c/buck,ilya-klyuchnikov/buck,OkBuilds/buck,OkBuilds/buck,Dominator008/buck,ilya-klyuchnikov/buck,tgummerer/buck,brettwooldridge/buck,mikekap/buck,grumpyjames/buck,facebook/buck,shs96c/buck,janicduplessis/buck,ilya-klyuchnikov/buck,zpao/buck,illicitonion/buck,zhan-xiong/buck,rowillia/buck,zhan-xiong/buck,SeleniumHQ/buck,grumpyjames/buck,clonetwin26/buck,rhencke/buck,romanoid/buck,romanoid/buck,kageiit/buck,SeleniumHQ/buck,zhan-xiong/buck,janicduplessis/buck,justinmuller/buck,grumpyjames/buck,illicitonion/buck,marcinkwiatkowski/buck,ilya-klyuchnikov/buck,nguyentruongtho/buck,bocon13/buck,rowillia/buck,shs96c/buck,shybovycha/buck,vine/buck,zhan-xiong/buck,rhencke/buck,bocon13/buck,shybovycha/buck,robbertvanginkel/buck,vschs007/buck,rowillia/buck,kageiit/buck,romanoid/buck,darkforestzero/buck,sdwilsh/buck,OkBuilds/buck,bocon13/buck,janicduplessis/buck,OkBuilds/buck,rmaz/buck,raviagarwal7/buck,dsyang/buck,vschs007/buck,LegNeato/buck,OkBuilds/buck,darkforestzero/buck,janicduplessis/buck,vine/buck,raviagarwal7/buck,mikekap/buck,shs96c/buck,mogers/buck,ilya-klyuchnikov/buck,illicitonion/buck,rmaz/buck,raviagarwal7/buck,daedric/buck,robbertvanginkel/buck,brettwooldridge/buck,Addepar/buck,rmaz/buck,rmaz/buck,justinmuller/buck,justinmuller/buck,robbertvanginkel/buck,rhencke/buck,shybovycha/buck,robbertvanginkel/buck,JoelMarcey/buck,illicitonion/buck,tgummerer/buck,LegNeato/buck,vine/buck,Addepar/buck,sdwilsh/buck,Distrotech/buck,clonetwin26/buck,janicduplessis/buck,raviagarwal7/buck,illicitonion/buck,Dominator008/buck,vine/buck,brettwooldridge/buck,robbertvanginkel/buck,robbertvanginkel/buck,romanoid/buck,tgummerer/buck,brettwooldridge/buck,zhan-xiong/buck,marcinkwiatkowski/buck,LegNeato/buck,liuyang-li/buck,dsyang/buck,zpao/buck,rowillia/buck,janicduplessis/buck,grumpyjames/buck,brettwooldridge/buck,rmaz/buck,darkforestzero/buck,shybovycha/buck,shs96c/buck,Distrotech/buck,romanoid/buck,ilya-klyuchnikov/buck,vschs007/buck,davido/buck,ilya-klyuchnikov/buck,mikekap/buck,k21/buck,davido/buck,rhencke/buck,grumpyjames/buck,rhencke/buck,dsyang/buck,davido/buck,darkforestzero/buck,k21/buck,shybovycha/buck,clonetwin26/buck,marcinkwiatkowski/buck,mogers/buck,brettwooldridge/buck,rowillia/buck,tgummerer/buck,rmaz/buck,romanoid/buck,vschs007/buck,JoelMarcey/buck,janicduplessis/buck,daedric/buck,raviagarwal7/buck,vschs007/buck,Distrotech/buck,daedric/buck,dsyang/buck,bocon13/buck,sdwilsh/buck,janicduplessis/buck,darkforestzero/buck,mikekap/buck,zhan-xiong/buck,LegNeato/buck,raviagarwal7/buck,shybovycha/buck,shybovycha/buck,darkforestzero/buck,clonetwin26/buck,justinmuller/buck,zhan-xiong/buck,LegNeato/buck,vschs007/buck,daedric/buck,nguyentruongtho/buck,zhan-xiong/buck,mikekap/buck,vschs007/buck,rmaz/buck,brettwooldridge/buck,bocon13/buck,marcinkwiatkowski/buck,SeleniumHQ/buck,rowillia/buck,robbertvanginkel/buck,k21/buck,vine/buck,mikekap/buck,justinmuller/buck,dsyang/buck,darkforestzero/buck,marcinkwiatkowski/buck,Dominator008/buck,illicitonion/buck,SeleniumHQ/buck,sdwilsh/buck,shs96c/buck,k21/buck,sdwilsh/buck,robbertvanginkel/buck,mogers/buck,mogers/buck,liuyang-li/buck,vschs007/buck,marcinkwiatkowski/buck,rowillia/buck,mikekap/buck,k21/buck,shs96c/buck,justinmuller/buck,janicduplessis/buck,JoelMarcey/buck,LegNeato/buck,bocon13/buck,romanoid/buck,Addepar/buck,ilya-klyuchnikov/buck,robbertvanginkel/buck,Dominator008/buck,shs96c/buck,robbertvanginkel/buck,tgummerer/buck,rmaz/buck,OkBuilds/buck,JoelMarcey/buck,dsyang/buck,SeleniumHQ/buck,raviagarwal7/buck,rowillia/buck,janicduplessis/buck,tgummerer/buck,facebook/buck,justinmuller/buck,SeleniumHQ/buck,Dominator008/buck,davido/buck,LegNeato/buck,JoelMarcey/buck,rowillia/buck,facebook/buck,dsyang/buck,justinmuller/buck,k21/buck,romanoid/buck,facebook/buck,liuyang-li/buck,grumpyjames/buck,sdwilsh/buck,vschs007/buck,davido/buck,darkforestzero/buck,mogers/buck,vine/buck,bocon13/buck,clonetwin26/buck,shs96c/buck,zhan-xiong/buck,davido/buck,SeleniumHQ/buck,shybovycha/buck