doc/effective_go.html: a little more about errors Make it a little clearer how they are used, in particular that it is not enough just to return a nil pointer on error, but also to return an error value explaining the problem.
doc/effective_go.html: a little more about errors
Make it a little clearer how they are used, in particular that
it is not enough just to return a nil pointer on error, but also
to return an error value explaining the problem.

Fixes issue 1963.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/97360045

sanjosh/sanjos100-tipc,webfd/go-zh,sanjosh/sanjos100-tipc,d0f/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,d0f/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh