Backport of docs: Add missing `&&` in DNS forwading tutorial into release/1.20.x (#21809)

backport of commit 3ba99fd382

Co-authored-by: Lens0021 / Leslie <lorentz0021@gmail.com>

website/content/docs/services/discovery/dns-forwarding/enable.mdx

@@ -66,7 +66,7 @@ When using the Consul Docker image, add the following to the environment to allo
 To avoid running Consul as a privileged user, the following `iptables` commands are sufficient to map port `53` to `8600` and redirect DNS queries to Consul.
 
 ```shell-session
-# iptables --table nat --append OUTPUT --destination localhost --protocol udp --match udp --dport 53 --jump REDIRECT --to-ports 8600 \
+# iptables --table nat --append OUTPUT --destination localhost --protocol udp --match udp --dport 53 --jump REDIRECT --to-ports 8600 && \
   iptables --table nat --append OUTPUT --destination localhost --protocol tcp --match tcp --dport 53 --jump REDIRECT --to-ports 8600
 ```