docs: add docs about network mode

[ngshiheng]

What is the problem I am trying to address?

• Added some documentation for Athens' Network Mode configuration
• Added some use cases for each network mode
• Fixed the "Fork me on GitHub" ribbon
• Fixed some broken links
• Updated helm CLI installation instruction

To run this locally, just check out this branch and run hugo serve -s docs at the repository root.

[ngshiheng]

@marwan-at-work can you help to take a look at this PR for docs update? I think you have the most context about Athens NetworkMode

[marwan-at-work]

This mode retrieves versions from Athens' storage only if the VCS fails.

I don't believe that's true. We always retrieve versions from the Athens storage. We just fallback to only providing this list in case of an upstream outage

[ngshiheng]

We always retrieve versions from the Athens storage

Hmm sorry, I don't exactly follow

1. This was taken from this snippet.
2. That aside, I can attest this behavior is correct based on existing live deployments
3. Also referring to /pkg/download/protocol.go

maybe I could have worded it better? 🤔

edit: AFAIK go get will reach out to VCS to retrieve versions. But commands like go mod download and go build will always return whatever that is from Athens storage

[ngshiheng]

@marwan-at-work WDYT? can you recommend what can I change here to move this PR forward?