Fixed formatting of existing note and transfered one from the reference/extension_types.rst.
Fixed formatting of existing note and transfered one from the reference/extension_types.rst.

scoder/cython,cython/cython,cython/cython,da-woods/cython,scoder/cython,da-woods/cython,scoder/cython,scoder/cython,cython/cython,da-woods/cython,da-woods/cython,cython/cython