Docs: missing documentation of macOS `gtar` requirement

[junhaoliao]

Bug

as the title suggests, we should have some docs to say gtar should be installed, as that's been required since #21

yscope-dev-utils version

92cc1f3

Environment

junhao@Junhaos-MBP ~ % sw_vers 
ProductName:		macOS
ProductVersion:		15.5
BuildVersion:		24F74

Reproduction steps

This was found as running task deps in y-scope/clp-ffi-js@13c31ed on mac fails.

# even with "--verbose", the cause of the command failure isn't very clear
junhao@1498777c24d1 clp-ffi-js % task deps --verbose
...
task: [utils:remote:download-and-extract-tar-/Users/junhao/workspace/clp-ffi-js/build/deps/ystdlib-src] gtar --extract --strip-components="1" --directory "/Users/junhao/workspace/clp-ffi-js/build/deps/ystdlib-src" --file "/Users/junhao/workspace/clp-ffi-js/build/deps/ystdlib-src.tar.gz" --no-anchored --wildcards 2> /dev/null
task: Failed to run task "deps:default": exit status 127

[junhaoliao]

in addition to docs (which we can't expect everyone reads), i believe we should add some utility tasks to print out the required deps' versions, which can be called in the init task of any user repo of yscope-dev-utils. If we can't even list the versions due to the commands being not found, developers can easily interpret the error messages and do corresponding actions. Printing out the versions will also aid debugging issues in various CI environments, where some of the deps come pre-installed and aren't managed by us.

[junhaoliao]

to install gtar: brew install gnu-tar