encoding/csv: document Read error behavior
encoding/csv: document Read error behavior

Fixes #17342.

Change-Id: I76af756d7aff464554c5564d444962a468d0eccc
Reviewed-on: https://go-review.googlesource.com/32172
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Quentin Smith <d6b8e48afb2534b213e391cab43016505747a234@golang.org>

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