doc: add SIGPIPE behaviour change to go1.8.txt
doc: add SIGPIPE behaviour change to go1.8.txt

CL 32796 changes the SIGPIPE behaviour for c-archive and c-shared
programs. Add it to go1.8.txt.

Change-Id: I31200187033349c642965a4bb077bcc77d5329a3
Reviewed-on: https://go-review.googlesource.com/33397
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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