Adding another good silient movie gif source

VideoColorizerColab.ipynb

@@ -226,6 +226,7 @@
     "---\n",
     "#⚙ Recommended video and gif sources \n",
     "* [/r/Nickelodeons/](https://www.reddit.com/r/Nickelodeons/)\n",
+    "* [r/silentmoviegifs](https://www.reddit.com/r/silentmoviegifs/)\n",
     "* https://twitter.com/silentmoviegifs "
    ]
   }