Add documentation to interface methods, improve readme

[Fluglow]

• Add short project description and installation guide to readme
• Add documentation to Lightsheet methods
• Make some internal methods private in Lightsheet

[rafinutshaw]

Just one question, we will have a seperate pr to write the whole readme.md file. right?

[Fluglow]

Just one question, we will have a seperate pr to write the whole readme.md file. right?

Yes, if someone has time to do it. I wanted to at least add the project description, since I think it's the most important part.