[examples] Add "Open in Colab" button to notebooks.

Author: ChrisCummins

examples/getting-started.ipynb

@@ -27,6 +27,10 @@
     "id": "AidRbcu8Pwxh"
    },
    "source": [
+    "<a href=\"https://colab.research.google.com/github/facebookresearch/CompilerGym/blob/stable/examples/getting-started.ipynb\">\n",
+    "    <img src=\"https://colab.research.google.com/assets/colab-badge.svg\" alt=\"Open in Colab\" height=\"20\">\n",
+    "</a>\n",
+    "\n",
     "# CompilerGym Getting Started\n",
     "\n",
     "CompilerGym is a toolkit for applying reinforcement learning to compiler optimization tasks. This document provides a short walkthrough of the key concepts, using the codesize reduction task of a production-grade compiler as an example. It will take about 20 minutes to work through. Lets get started!"

examples/rllib.ipynb

@@ -22,6 +22,10 @@
     "id": "gsrdt9HooN9K"
    },
    "source": [
+    "<a href=\"https://colab.research.google.com/github/facebookresearch/CompilerGym/blob/stable/examples/rllib.ipynb\">\n",
+    "    <img src=\"https://colab.research.google.com/assets/colab-badge.svg\" alt=\"Open in Colab\" height=\"20\">\n",
+    "</a>\n",
+    "\n",
     "# Using CompilerGym environments with RLlib\n",
     "\n",
     "In this notebook we will use [RLlib](https://docs.ray.io/en/master/rllib.html) to train an agent for CompilerGym's [LLVM environment](https://facebookresearch.github.io/CompilerGym/llvm/index.html). RLlib is a popular library for scalable reinforcement learning, built on [Ray](https://docs.ray.io/en/master/index.html). It provides distributed implementations of several standard reinforcement learning algorithms.\n",