docs: add a note for dns command

License: MIT
Signed-off-by: Overbool <overbool.xu@gmail.com>

core/commands/dns.go

@@ -32,6 +32,10 @@ remember.  To create memorable aliases for multihashes, DNS TXT
 records can point to other DNS links, IPFS objects, IPNS keys, etc.
 This command resolves those links to the referenced object.
 
+Note: This command can only recursively resolve DNS links,
+it will fail to recursively resolve through IPNS keys etc.
+For general-purpose recursive resolution, use ipfs name resolve -r.
+
 For example, with this DNS TXT record:
 
 	> dig +short TXT _dnslink.ipfs.io