Explain the difference between higlighting and listAnnotations better

[alkatar21]

For me it was not immediately clear from the README that higlighting and listAnnotations do not work the same way and so I had expected at first that everything that is higlighted also appears in the list.
While the former works in all files, even in the settings, listAnnotations respects todohighlight.include and todohighlight.exclude and is more or less an own independent function.

I would suggest the following options:

• In the README, emphasize more strongly that these are 2 more or less different features. Maybe also mark the options accordingly.
• higlighting also respects these settings.
  Thus the extension could start in a further step only if a corresponding file type is called and improves thereby also the VSCode startup time.

[jlopes26]

yap, I was just right to open a issue when I saw this and then understand the reason why the listAnnotations "didn't work"
Just added the extension .cs to the included and it worked right away

//thanks Jonathan Clark for the fork and all the hard work