doc/installing: Mention installing Go from upstream

Signed-off-by: Stéphane Graber <stgraber@stgraber.org>
Suggested-by: AJRepo <AJRepo@users.noreply.github.com>

doc/installing.md

@@ -290,6 +290,8 @@ Install the build and required runtime dependencies with:
     sudo apt update
     sudo apt install acl attr autoconf automake dnsmasq-base git golang-go libacl1-dev libcap-dev liblxc1 lxc-dev libsqlite3-dev libtool libudev-dev liblz4-dev libuv1-dev make pkg-config rsync squashfs-tools tar tcl xz-utils ebtables
 
+****NOTE:**** The version of `golang-go` in your version of Debian or Ubuntu may not be sufficient to build Incus (see {ref}`requirements-go`).
+In such cases, you may need to install a newer Go version [from upstream](https://go.dev/doc/install).
 
 There are a few storage drivers for Incus besides the default `dir` driver.
 Installing these tools adds a bit to initramfs and may slow down your