fixed ref to individual html files

[fotinidelig]

Minor fix, but since it was found I fixed it.

Command-Reference.html was using the wrong ref to the individual HTML file names.
Should be working as intended now & was checked locally.

[jooste]

Hi @fotinidelig,

Thanks for finding this issue. However, the html files are automatically generated from markdown files. To properly fix this we therefore either need to change the md files (which come from the github wiki), or perhaps it can be arranged with some parameter to the conversion script (pandoc).