update Chapter11

Author: Qiuping Xu

Chapter_11_sec_11.8.ipynb

@@ -31,7 +31,7 @@
    "outputs": [],
    "source": [
     "\"\"\" \n",
-    "I am also new to this topic, let us learn those concept together. \n",
+    "I am also new to this topic, so let us learn those concept together. Feedbacks are welcome.\n",
     "Survival analysis is a statistical method used to estimate the survival function of a population.\n",
     "These arise in the analysis of a unique kind of outcome variable: the analysis time until an event occurs.\n",
     "\"\"\""