Referring to URL of lectures does not work

[sayaikegawa]

Hi @mmcky ,

In lectures, it often refers to other lectures and codes written in own lecture. However, this does not work in all lectures in myst.
(referring to Wikipedia or other website works ok)

For example:
in An introductory Example, it refers to Numpy. So, Numpy should be written blue like below in current website

however, in netlify.app,

In rst file:

The first line imports :doc:`NumPy <numpy>`, a favorite Python package for tasks like

But in Myst: <numpy> is dropped.

The first line imports NumPy, a favorite Python package for tasks like

[mmcky]

thanks @sayaikegawa this is now fixed in #21