podman-login: add page

[cyqsimon]

• [x] The page(s) are in the correct platform directories: common, linux, osx, windows, sunos, android, etc.
• [x] The page(s) have at most 8 examples.
• [x] The page description(s) have links to documentation or a homepage.
• [x] The page(s) follow the content guidelines.
• [x] The page(s) follow the style guide.
• [x] The PR title conforms to the recommended templates.
• Version of the command being documented (if known): 5.3.0

[cyqsimon]

Hi. Have you thought about spliting this page into linux and common version to make descriptions more clear?

Yeah this thought did go through my head but ultimately I decided against it. These are the main reasons:

• They are fundamentally the same subcommand within the same binary. Login persistence is the only platform-dependent difference.
• Having two pages increases maintenance burden, especially if someone adds more examples in the future.
• Podman is a tool primarily intended to run on Linux (on Windows or macOS it actually proxies most of its actions to a Linux VM). A significant proportion of users will likely be using it on Linux directly after using it for development on their personal non-Linux computers, so it would be wise to inform them of this important difference when they first look it up on their personal computers.

So I'm inclined to keep it as is. Hopefully you understand.

[cyqsimon]

Thanks all; excellent recommendations. Committed.