Consider making stand-alone installation easier on Linux & Windows

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Is your feature request related to a problem? Please describe.
While reviewing the poly install docs, I noticed there can be quite a few manual steps for stand-alone installation for Linux and Windows. This might be overwhelming to a newcomer.

Describe the solution you'd like
On other projects, I've seen the use of install scripts.

For examples:

• deps.clj has an install script for macOS/Linux and an install.ps1 for Windows.
• clj-kondo does something similar (although it uses scoop for Windows).
• babashka recommends brew for both macos/Linux.

For all the above, manual download is also an option.

Another benefit of an install script is that it can also do a checksum on anything it downloads.

Describe alternatives you've considered
Consider describing brew as an option for Linux.
Consider creating something on scoop for Windows.

Additional context
Poly stand-alone has 2 assets: the jar and the launcher script.
The launcher scripts could be generated by the installer and/or made available for manual download from a set of release assets.

If I remember correctly, the lein script will actually download any necessary assets, so that might another place to look for inspiration.

[lread]

Additional note: While reviewing the upgrade docs, I think that whatever solution covers poly installation should also consider poly upgrade.