document how to create measurements & annotations

[abubelinha]

This might sound ridiculous, my initial issue was that you don't explain how to use the main features of this plugin.

In your demo I see the menu to display the grid and rotate it.
I see the menu to select annotations color, reset them, export ...

But I can't color, reset or export any annotations/measurements because I don't know how to create them.
Should I click any key while I drag my mouse?
I don't see any explanation on how to do that.

Thanks a lot
@abubelinha

EDIT: One hour later I discovered by chance that clicking shift+dragging mouse lets me draw an annotation box.
But I still can't measure things in the image.

BTW, regarding annotation boxes, this might be a bug: At some point, that shift+drag combination stops working and I cannot draw annotation boxes anymore. I am still not sure when that happens (probably after some other key combination when I tried to measure things).

EDIT: Later on, I discovered that double clicking I can draw measure start point, and doing the same I can draw measure end point.

So I changed issue title. Please add this info to README.md

Thanks a lot for this plugin!
@abubelinha

[verrochi92]

Hi abubelinha, thank you for your interest in our project. I will update the documentation to include this, thank you for pointing it out. I'll look into what's happening with annotations as well.