DOC: quic: Add "limited-quic" new tuning setting

Document "limited-quic" new tuning setting which must be used to
enable the QUIC listener bindings when haproxy is compiled against
a TLS/SSL stack without QUIC support.

doc/configuration.txt

@@ -1797,6 +1797,13 @@ issuers-chain-path <dir>
   "issuers-chain-path" directory. All other certificates with the same issuer
   will share the chain in memory.
 
+limited-quic
+  This setting must be used to explicitly enable the QUIC listener bindings when
+  haproxy is compiled against a TLS/SSL stack without QUIC support, typically
+  OpenSSL. It has no effect when haproxy is compiled against a TLS/SSL stack
+  with QUIC support, quictls for instance. Note that QUIC 0-RTT is not supported
+  when this setting is set.
+
 localpeer <name>
   Sets the local instance's peer name. It will be ignored if the "-L"
   command line argument is specified or if used after "peers" section