Documented SyncVar
Documented SyncVar

Since we used it in the DocRunner and noticed it could have better
documentation.

Review by @heathermiller.

jvican/scala,jvican/scala,felixmulder/scala,slothspot/scala,slothspot/scala,lrytz/scala,felixmulder/scala,martijnhoekstra/scala,shimib/scala,lrytz/scala,scala/scala,lrytz/scala,jvican/scala,scala/scala,lrytz/scala,scala/scala,martijnhoekstra/scala,shimib/scala,lrytz/scala,jvican/scala,shimib/scala,slothspot/scala,jvican/scala,felixmulder/scala,martijnhoekstra/scala,lrytz/scala,scala/scala,slothspot/scala,felixmulder/scala,shimib/scala,felixmulder/scala,felixmulder/scala,martijnhoekstra/scala,slothspot/scala,jvican/scala,slothspot/scala,scala/scala,shimib/scala,jvican/scala,martijnhoekstra/scala,shimib/scala,scala/scala,martijnhoekstra/scala,felixmulder/scala,slothspot/scala