DOC: Remove requirement of lower-casing section links

Sphinx seems to lowercase internally, so this isn't necessary.

Author: mgeier

doc/markdown-cells.ipynb

@@ -263,7 +263,6 @@
     "\n",
     "Sphinx section anchors are different from Jupyter section anchors!\n",
     "To create a link to a subsection in an `.rst` file (or another non-notebook source file), you not only have to replace spaces with hyphens, but also slashes and some other characters.\n",
-    "Furthermore, you have to change the whole section title to lowercase letters.\n",
     "In case of doubt, just check the target HTML page generated by Sphinx.\n",
     "\n",
     "</div>"