Add Basic Documentation to README.md

[tavaughan]

At minimum:

• A brief 1-paragraph description of what the module does
• A few screenshots showing the main features
• Use cases
• Explanation of input options, parameters, etc.

[tavaughan]

@lassoan Do we have any nice screenshots of use cases?

[lassoan]

You can add some for LumpNav and your catheter tracking. I'll get some heart annulus contours.

[tavaughan]

@lassoan I added tumor segmentation and catheter reconstruction use cases. If you have anything else you want to add, please do :-). If not, please close this ticket.

[tavaughan]

@lassoan