doc: mention concurrent map write/iterate detector
doc: mention concurrent map write/iterate detector

Mention that the best-effort race detector on maps
was upgraded to detect write/iterate races.

Fixes #18137

Change-Id: Ib6e0adde47e965126771ea712386031a2a55eba3
Reviewed-on: https://go-review.googlesource.com/33768
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

codestation/go,CAFxX/go,CAFxX/go,josharian/go,nawawi/go,golang/go,akutz/go,polyverse-security/go,derekmarcotte/go,linux-on-ibm-z/go,Cofyc/go,cloudflare/go,golang/go,linux-on-ibm-z/go,golang/go,Cofyc/go,suncycheng/go,linux-on-ibm-z/go,derekmarcotte/go,akutz/go,derekmarcotte/go,nawawi/go,codestation/go,josharian/go,polyverse-security/go,golang/go,vsekhar/elastic-go,Cofyc/go,vsekhar/elastic-go,cloudflare/go,Cofyc/go,CAFxX/go,linux-on-ibm-z/go,josharian/go,vsekhar/elastic-go,linux-on-ibm-z/go,nawawi/go,cloudflare/go,ImJasonH/go,golang/go,linux-on-ibm-z/go,polyverse-security/go,CAFxX/go,polyverse-security/go,polyverse-security/go,suncycheng/go,ImJasonH/go,derekmarcotte/go,derekmarcotte/go,CAFxX/go,akutz/go,nawawi/go,vsekhar/elastic-go,codestation/go,polyverse-security/go,derekmarcotte/go,CAFxX/go,nawawi/go,nawawi/go,cloudflare/go,akutz/go,ImJasonH/go,ImJasonH/go,Cofyc/go,derekmarcotte/go,Cofyc/go,suncycheng/go,nawawi/go,cloudflare/go,polyverse-security/go,codestation/go,ImJasonH/go,codestation/go,akutz/go,CAFxX/go,akutz/go,Cofyc/go,christopher-henderson/Go,polyverse-security/go,suncycheng/go,cloudflare/go,Cofyc/go,josharian/go,derekmarcotte/go,golang/go,vsekhar/elastic-go,suncycheng/go,josharian/go,vsekhar/elastic-go,linux-on-ibm-z/go,akutz/go,cloudflare/go,cloudflare/go,vsekhar/elastic-go,linux-on-ibm-z/go,ImJasonH/go,golang/go,josharian/go,nawawi/go,suncycheng/go,ImJasonH/go,golang/go,akutz/go,ImJasonH/go,suncycheng/go,josharian/go,josharian/go,codestation/go,vsekhar/elastic-go,codestation/go,CAFxX/go,suncycheng/go,codestation/go