update ip_prefixes docs

we cant actually have arbitrary ip ranges, add a note about that.

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

Author: kradalby

config-example.yaml

@@ -63,6 +63,11 @@ noise:
 # List of IP prefixes to allocate tailaddresses from.
 # Each prefix consists of either an IPv4 or IPv6 address,
 # and the associated prefix length, delimited by a slash.
+# While this looks like it can take arbitrary values, it
+# needs to be within IP ranges supported by the Tailscale
+# client.
+# IPv6: https://github.com/tailscale/tailscale/blob/22ebb25e833264f58d7c3f534a8b166894a89536/net/tsaddr/tsaddr.go#LL81C52-L81C71
+# IPv4: https://github.com/tailscale/tailscale/blob/22ebb25e833264f58d7c3f534a8b166894a89536/net/tsaddr/tsaddr.go#L33
 ip_prefixes:
   - fd7a:115c:a1e0::/48
   - 100.64.0.0/10