doc/install: add openbsd
doc/install: add openbsd

Add openbsd to the $GOOS list.

R=golang-dev, r, rsc
CC=golang-dev
http://codereview.appspot.com/4964053

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

Triskite/willstone-goclone,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,bryanxu/go-zh,Triskite/willstone-goclone,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,webfd/go-zh,rdp/rogerpack2005-golang,scirelli/scirelli-go,mhennings/marcohennings-go,scirelli/scirelli-go,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,sanjosh/sanjos100-tipc,webfd/go-zh,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,webfd/go-zh,Triskite/willstone-goclone,scirelli/scirelli-go,d0f/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,rflanagan/reginaldflanagan-project1,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,d0f/go-zh,Triskite/willstone-goclone,mhennings/marcohennings-go,mhennings/marcohennings-go,glycerine/jeaten-go-arrayof-structof,Triskite/willstone-goclone,scirelli/scirelli-go,rflanagan/reginaldflanagan-project1,glycerine/jeaten-go-arrayof-structof,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,d0f/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,webfd/go-zh,webfd/go-zh,d0f/go-zh,d0f/go-zh,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,webfd/go-zh,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,mhennings/marcohennings-go,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,bryanxu/go-zh,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,scirelli/scirelli-go,bryanxu/go-zh,scirelli/scirelli-go