cmd/vet/all/whitelist: add readme.txt
cmd/vet/all/whitelist: add readme.txt

This was written for CL 27811,
but it got lost in the sea of new files.

Change-Id: I5c52cb23dda499b21a6bb32ed5c586779ccbc2f1
Reviewed-on: https://go-review.googlesource.com/28960
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

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