Merge pull request CamDavidsonPilon#47 from alexgarel/precise-phi

precise what phi means in appendix

Author: CamDavidsonPilon

Chapter4_TheGreatestTheoremNeverTold/LawOfLargeNumbers.ipynb

@@ -991,6 +991,8 @@
       "\n",
       "$$ 0.05 = \\Phi\\left( \\frac{(x - \\mu)}{\\sigma}\\right) $$ \n",
       "\n",
+      "$\\Phi$ being the [cumulative distribution for the normal distribution](http://en.wikipedia.org/wiki/Normal_distribution#Cumulative_distribution)\n",
+      "\n",
       "\n",
       "\n",
       "\n"