Add a less formal introduction of FMM and what it can be used for in the README

[kopytjuk]

As a new user it is probably non-trivial to grasp what FMM is and what the library tries to solve despite being incredibly useful in multiple domains like seismic research, acid flow, motion planning etc.

A good introduction is provided by Berkeley here. Usual applications are:

• Image segmentation in medicine (see here)
• Route planning (see here)
• Motion planning in challenging terrain (see here)

Would it help to extend the README to provide a user an idea what the library could be used for?

[jkfurtney]

Hi Marat, Thanks for getting in touch. Yes, this is a good idea, Can you submit a pull request with a modified README? Thanks