doc: Add bind9-dnsutils to testsuite requirements

Signed-off-by: Thomas Hipp <thomas.hipp@canonical.com>

Author: monstermunchkin

doc/index.md

@@ -56,7 +56,7 @@ sudo apt install btrfs-progs
 To run the testsuite, you'll also need:
 
 ```bash
-sudo apt install curl gettext jq sqlite3 uuid-runtime socat
+sudo apt install curl gettext jq sqlite3 uuid-runtime socat bind9-dnsutils
 ```
 
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