New-ExternalHelp should handle "markdown lists" in "Related Links" section

[Matteo-T]

Steps to reproduce

1. Have your .md with a section like

   - [Link1](link1.md)
   - [Link2](link2.md)

2. Run the New-ExternalHelp cmdlet to generate the offline documentation for the module

Expected behavior

Some error message

Actual behavior

It should just work (recognize the leading " - " and throw it away