Remove zsh; move manual from Linux to the top

Author: alexandear

docs/src/docs/welcome/integrations.mdx

@@ -52,14 +52,9 @@ The following plugins support `golangci-lint`:
 
 `golangci-lint` can generate Bash, fish, PowerShell, and Zsh completion files.
 
-### macOS
-
-#### Zsh
-
-To use `golangci-lint` completion on macOS with `zsh`, which is the default shell since Catalina,
-follow the instructions on `golangci-lint completion zsh --help`.
+See the instructions on `golangci-lint completion <YOUR_SHELL> --help` (replace `<YOUR_SHELL>` with your favorite one).
 
-#### Bash
+### macOS
 
 There are two versions of `bash-completion`, v1 and v2. V1 is for Bash 3.2 and v2 is for Bash 4.1+. The `golangci-lint` completion script doesn’t work correctly with bash-completion v1 and Bash 3.2. It requires bash-completion v2 and Bash 4.1+. Thus, to be able to correctly use `golangci-lint` completion on macOS, you have to install and use Bash 4.1+ ([instructions](https://itnext.io/upgrading-bash-on-macos-7138bd1066ba)). The following instructions assume that you use Bash 4.1+ (that is, any Bash version of 4.1 or newer).
 
@@ -80,10 +75,6 @@ echo 'source <(golangci-lint completion bash)' >>~/.bashrc
 source ~/.bashrc
 ```
 
-### Linux
-
-See the instructions on `golangci-lint completion <YOUR_SHELL> --help` (replace `<YOUR_SHELL>` with your favorite one).
-
 ## CI Integration
 
 See our [GitHub Action](/welcome/install/#github-actions).