Update package.json & add brain-gcd game demo run to readme

Author: thedoorbell

README.md

@@ -11,3 +11,7 @@
 ### brain-calc demo run
 
 <https://asciinema.org/a/TNtcu8r12ZyfsE9b1UGn45JZL>
+
+### brain-gcd demo run
+
+<https://asciinema.org/a/8BwBf9NXrmHYz8WeA9PxtH6cG>

package.json

@@ -20,7 +20,8 @@
   "bin": {
     "brain-games": "bin/brain-games.js",
     "brain-even": "bin/brain-even.js",
-    "brain-calc": "bin/brain-calc.js"
+    "brain-calc": "bin/brain-calc.js",
+    "brain-gcd": "bin/brain-gcd.js"
   },
   "dependencies": {
     "readline-sync": "^1.4.10"