Documentation says that custom linters are enabled with --enable-all, but they are not

[misha-ridge]

Welcome

• Yes, I'm using a binary release within 2 latest major releases. Only such installations are supported.
• Yes, I've searched similar issues on GitHub and didn't find any.
• Yes, I've included all information below (version, config, etc.).
• Yes, I've tried with the standalone linter if available (e.g., gocritic, go vet, etc.). (https://golangci-lint.run/usage/linters/)

Description of the problem

Documentation for custom linters says "Custom linters are enabled by default".

However this is not the case, and this confuses people: #3080, #3085, and I also spent half a day debugging why the custom linter is not enabled.

Version of golangci-lint

```master```

Configuration file

N/A

Go environment

N/A

Verbose output of running

N/A

Code example or link to a public repository

N/A