Update readme, doesn't work with "math blocks"

[Kalthorn]

Hi, just in case it saves someone else the frustration and confusion, please consider updating your readme to call our the fact that the plugin uses/requires it's own special blocks, not math blocks.

I spent five minutes working inside a (right-click->insert->math block) and it never once worked. Ideally they would work with the built-in code blocks but if not, please specifically call that out in the readme/docs.

Sorry if this has been covered elsewhere or if it's the result of growing pains between the app and the plugin (like maybe math blocks weren't built-in until recently).

[Kalthorn]

Adding a hearty "thank-you!" for the work you've done :)