Add google colab link to the example nb (#36)

examples/rag_eval_harness.ipynb

@@ -6,6 +6,8 @@
         "id": "03ixktWsySVK"
       },
       "source": [
+        "<a href=\"https://colab.research.google.com/github/deepset-ai/haystack-experimental/blob/main/examples/rag_eval_harness.ipynb\" target=\"_parent\"><img src=\"https://colab.research.google.com/assets/colab-badge.svg\" alt=\"Open In Colab\"/></a>\n",
+        "\n",
         "# Evaluating RAG Pipelines with EvaluationHarness\n",
         "\n",
         "In this notebook, you'll learn how to use the [`EvaluationHarness`](https://docs.haystack.deepset.ai/v2.3-unstable/reference/evaluation-harness#evaluationharness) from the [haystack-experimental](https://github.com/deepset-ai/haystack-experimental) repository to assess the performance of Retrieval-Augmented Generation (RAG) pipelines over the [SQUAD dataset](https://huggingface.co/datasets/rajpurkar/squad_v2).\n",