Add a dedicated guide on error handling (err vs res.IsError())

[eduardolat]

Hey folks, first off, awesome library!

I'm opening this issue to suggest a documentation improvement. I think it would be super helpful for new users to have a dedicated page on resty.dev (and maybe linked in the README) that's all about error handling.

For a beginner, it can be pretty confusing to figure out the difference between the two main ways an error can happen.

1. The err returned from the request:

   res, err := client.R().Get("https://example.com")
   if err != nil {
     // What kind of error is this? (e.g., connection failed, DNS, timeout)
   }

2. The res.IsError() check:

   if res.IsError() {
     // And what kind of error is this? (e.g., 404, 500)
   }

A new user might see err == nil and assume everything worked, but they might have actually received a 500 Internal Server Error. Or, they might get a connection error where err != nil, and then try to check res.IsError()

Having a "Error Handling" page would be amazing. It could clearly explain:

• When err will be non-nil (client-side problems, connection issues, timeouts, marshalling errors, etc.).
• When res.IsError() will be true (server-side problems, 4xx/5xx status codes).
• The recommended "best practice" way to check for both conditions to safely handle all possible errors.
• Basically, a guide for everything related to errors

I think this would clear up a lot of confusion and help people get started more smoothly.

Thanks for considering it!

[jeevatkm]

@eduardolat Thanks for bringing it out. It's a good improvement for everyone, not just beginners. I will work on improving v3 documentation.

Resty uses Hugo for the docs. If you're interested in creating the first version of this page, you can submit a PR here - https://github.com/go-resty/docs