Add support for aarch64

[openjck]

Thanks for the great project. I use docopts everywhere.

Unfortunately, it doesn't appear to support aarch64, so I'm unable to use my shell scripts on Raspberry Pi. When trying to install it, I encountered this error:

ERROR                                                                                                                   
Fri Jan 23 11:23:04 PM EST 2026                                                                                         
OSTYPE not supported yet, or missing arch: aarch64                                                                      
or download failure.

You cat create an issue here: https://github.com/docopt/docopts/issues/

URL=https://github.com/docopt/docopts/releases/download/v0.6.4-with-no-mangle-double-dash/docopts_linux_
OSTYPE=linux-gnu
ARCH=aarch64
ARCH_BIN=
getconf LONG_BIT 64
RELEASE=v0.6.4-with-no-mangle-double-dash

Assuming it's easy (maybe it isn't), it would be great to have an aarch64 build.

[openjck]

I'm sorry, it looks like I'm mistaken. There is an ARM build, and it works on my Raspberry Pi, but the get_docopts.sh script doesn't download it when the architecture is reported as aarch64. I'll open a pull request momentarily.