Add documentation

[rguliev]

• Add auto doc generation using mkdocs + mkgendocs + mkdocs-material (a good example can be found in this repo)
• Add a general introduction with the context of the repository
• Add specific subsections (see hyperSpec docs for an example):
  • creating, filtering, combining, and changing the data
  • arithmetic operations
  • working with wavelenghts (interpolation and other)
  • aggregation and applying function
  • baseline correction
  • normalization
  • spike removal
  • plotting