DOC: adjust QUIC instruction in INSTALL

enable-tls1_3 is default, no need to specify it. make "libdir" explicit,
later example uses "lib" which was changed in 3.0.1 to "lib64"
diff --git a/INSTALL b/INSTALL
index f9d94f3..4dc9326 100644
--- a/INSTALL
+++ b/INSTALL
@@ -400,7 +400,7 @@
 repository is available at https://github.com/quictls/openssl. You can use the
 following instruction to build a functional QUICTLS.
 
-  $ ./config enable-tls1_3 [--prefix=/opt/quictls]
+  $ ./config --libdir=lib [--prefix=/opt/quictls]
   $ make
   $ make install