Add info about where to find and install the CLI (or other options)

[stockholmux]

topics/cli.md is descriptive of the CLI but I don't think it makes the connection for users that it's bundled with the server package. Lots of folks need to use the CLI but consume Valkey through a container or service so they don't have the Valkey itself installed on their workstations.

So, this section needs to give an example of how to:

1. Get it by building from source
2. Run valkey-cli from a container
3. Use something like memurai-cli on Windows machines.
4. Install the standalone CLI package in some distros (e.g. alpine)