Add note to tutorial about RuntimeWarnings

doc/tutorial.ipynb

@@ -171,7 +171,7 @@
    "source": [
     "## Calculate DIP rates and parameters\n",
     "\n",
-    "These two operations can be done in two lines of code (plus imports)."
+    "These two operations can be done in two lines of code (plus imports). Note that you may see `RuntimeWarning` messages, which indicates that some dose response curves were not able to be fitted. This can happen if the cells do not die in response to drug, the response is not closely approximated by a log-logistic curve, or the data are very noisy."
    ]
   },
   {