Just released a big update to the Sourcegraph Chrome extension that adds support for annotating GitHub PRs and diffs with jump-to-def links. This was by far the #1 user request. Direct link: https://chrome.google.com/webstore/detail/sourcegraph-for-github/dgjhfomjieaadpoljlnidmbgkdffpack.
The post a few weeks ago https://lobste.rs/s/xljhkx/browse_github_like_ide_jump_def_doc was for the initial release, to add IDE-like features when browsing files (not PRs) on GitHub.
Do you still only support java / go?
Yes, we currently support Java and Go but new languages are coming very soon.