VHS_NO_SANDBOX ENV option needs documented

[shaunco]

After banging my head against the wall on the on this error:

could not launch browser: [launcher] Failed to get the debug url: [0719/182133.729582:FATAL:zygote_host_impl_linux.cc(127)]
No usable sandbox! Update your kernel or see https://chromium.googlesource.com/chromium/src/+/main/docs/linux/suid_sandbox_development.md 
for more information on developing with the SUID sandbox. If you want to live dangerously and need an 
immediate workaround, you can try using --no-sandbox.

I came across #45 which is referenced by #195 which was merged over 2 years ago, and added VHS_NO_SANDBOX but doesn't seem to be documented anywhere outside of that PR.

For server mode, env options are documented in the readme ( https://github.com/charmbracelet/vhs/blob/main/README.md#the-vhs-server )...