README: Add cmake as dependency

Author: Grazfather

README.md

@@ -10,7 +10,7 @@ Building
 
 Usercorn depends on Go 1.6 or newer, as well as the latest unstable versions of Capstone, Unicorn, and Keystone.
 
-`make deps` will attempt to install all of the above dependencies into the source tree under `deps/`.
+`make deps` (requires `cmake`) will attempt to install all of the above dependencies into the source tree under `deps/`.
 
 `make` will update Go packages and build `usercorn`