doc/faq: explain why goroutines are anonymous
doc/faq: explain why goroutines are anonymous

Fixes #22770.

Change-Id: Ief62043fb6895e215d2530d2a3bf88f7ea58c875
Reviewed-on: https://go-review.googlesource.com/80195
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/go,Cofyc/go,cloudflare/go,cloudflare/go,akutz/go,golang/go,akutz/go,codestation/go,Cofyc/go,akutz/go,CAFxX/go,codestation/go,cloudflare/go,nawawi/go,akutz/go,CAFxX/go,cloudflare/go,codestation/go,josharian/go,codestation/go,christopher-henderson/Go,josharian/go,codestation/go,Cofyc/go,akutz/go,cloudflare/go,nawawi/go,golang/go,CAFxX/go,josharian/go,akutz/go,golang/go,Cofyc/go,Cofyc/go,cloudflare/go,cloudflare/go,josharian/go,codestation/go,nawawi/go,nawawi/go,nawawi/go,golang/go,CAFxX/go,akutz/go,Cofyc/go,CAFxX/go,josharian/go,akutz/go,josharian/go,josharian/go,nawawi/go,cloudflare/go,nawawi/go,nawawi/go,golang/go,CAFxX/go,golang/go,CAFxX/go,golang/go,codestation/go,codestation/go,josharian/go,CAFxX/go,Cofyc/go,Cofyc/go