Mention Qt in README

[skip ci]
diff --git a/doc/install/README.md b/doc/install/README.md
index 071a5d6..3bc4d35 100644
--- a/doc/install/README.md
+++ b/doc/install/README.md
@@ -26,6 +26,7 @@
     * Boost 1.56.0
     * libevent (optional, to build the nonblocking server)
     * zlib (optional)
+    * Qt (optional)
 * Java
     * Java 1.8
     * Gradle