For Mac OS X at least:
$ brew update && brew install ctags
$ alias ctags=/usr/local/Cellar/ctags/5.8/bin/ctags
$ cd $GOPATH/src/github.com/deis/deis
$ ctags -R .
Then in atom, type [Opt]+[Cmd]+[down arrow] when the cursor is on an identifier.
I found this info at atom/symbols-view#9
But ctags 5.8 doesn't understand Go! So edit ~/.ctags and add these lines:
--langdef=Go
--langmap=Go:.go
--regex-Go=/func([ \t]+\([^)]+\))?[ \t]+([a-zA-Z0-9_]+)/\2/f,func/
--regex-Go=/var[ \t]+([a-zA-Z_][a-zA-Z0-9_]+)/\1/v,var/
--regex-Go=/type[ \t]+([a-zA-Z_][a-zA-Z0-9_]+)/\1/t,type/