BUILD: Makefile: add the USE_QUIC option to make help

Add the missing "USE_QUIC" option to `make help`.

Must be backported as far as 2.4.

(cherry picked from commit 1b5f9de1b42d43cdd269690328fbb33875c93a8c)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/Makefile b/Makefile
index 11096c2..d08edb4 100644
--- a/Makefile
+++ b/Makefile
@@ -33,6 +33,7 @@
 #   USE_GETADDRINFO      : use getaddrinfo() to resolve IPv6 host names.
 #   USE_OPENSSL          : enable use of OpenSSL. Recommended, but see below.
 #   USE_OPENSSL_WOLFSSL  : enable use of wolfSSL with the OpenSSL API
+#   USE_QUIC             : enable use of QUIC with the quictls API (quictls, libressl, boringssl)
 #   USE_ENGINE           : enable use of OpenSSL Engine.
 #   USE_LUA              : enable Lua support.
 #   USE_ACCEPT4          : enable use of accept4() on linux. Automatic.