Add option to suppress Discord promo in installer output

Summary

Both install.sh and install.ps1 always print this line at the end of a successful install:

Stuck? Join our Discord https://discord.gg/deno

There is currently no way to suppress it.

Motivation

Some downstream projects invoke the official installer programmatically (e.g. during their own bootstrap/init flow) and want clean, product-branded output without third-party community links.

Concrete example: fount depends on Deno but is, in a sense, a competing chat/community platform. Showing a Discord invite during fount's first-run install is confusing at best and unwelcome for users who deliberately avoid Discord.

This is not about removing Discord support from Deno itself — only about making the installer script output configurable, similar to the existing --no-modify-path flag in install.sh.

Proposed behavior

Add an opt-out, for example:

Shell (install.sh):

curl -fsSL https://deno.land/install.sh | sh -s -- -y --no-discord-promo

PowerShell (install.ps1):

$env:DENO_INSTALL_NO_DISCORD_PROMO = "1"
irm https://deno.land/install.ps1 | iex

Or a single env var honored by both scripts, e.g. DENO_INSTALL_QUIET=1, if you prefer fewer flags.

When set, skip the final Discord line; keep the useful lines (Deno was installed successfully…, Run 'deno --help'…).

Context

• install.sh already documents flags like --no-modify-path and -y / --yes.
• install.ps1 has no equivalent flags today; an env var may be the least invasive addition there.

Thanks for considering this.

Start by reading install.sh, especially its existing --no-modify-path and -y/--yes handling, then inspect install.ps1 and the final Discord output in both scripts. Define the chosen opt-out interface and verify that it suppresses only the Discord line while retaining the successful-install and help messages in each installer.