Update GOcean documentation to talk about dl_esm_inf submodule

[arporter]

#223 has added dl_esm_inf as a git submodule. However, the user-guide still talks about the GOcean library hosted on puma. In this issue we will correct this. We will also move documentation of the GOcean library over to the dl_esm_inf repo.

[arporter]

Created gocean_doc_update branch.

[arporter]

#2470 has now updated the user guide so that part is done. However, the documentation of dl_esm_inf still needs moving over to that repo.