Clearify the cross platform nature of commands of verifying SSH/GPG keys

[typed-sigterm]

Description

It still cannot work properly in PowerShell, which supports |. (there may be some technical reasons here, but I am not a shell expert)
...so I think it is necessary to clarify on the Web UI that "git bash must be used on Windows".

Link #31858.

Screenshots

(not applicable)

Gitea Version

1.23.1

Can you reproduce the bug on the Gitea demo site?

Yes

Operating System

No response

Browser Version

Edge 132.0.2957.115