Making the project build with Qt5 and refactor README.md

[raydelto]

The project as it is, isn't building with Qt5. I made minor changes in order to make it build with Qt5. Also, the README file is not written in markdown format, so I renamed it from README to README.md and I reworded it to make it easier to understand.

[dimkanovikov]

Hello, my friend!

Thanks for your PR. It's great!

One thing I'd love to ask you improve - since, you change example to using QMainWindow it will be better to create the table widget itself on the heap.