Feature/readme

[j-ti]

Fixes #156

Changes proposed in this pull request:

• Add introduction from RTD
• Add badges for package build and doc
• State package install
• Rearrange example section and add Subtitles

The following steps were realized (required):

• [x] Correct linting with flake8 path_to_script
• [x] Check if tests pass locally with python -m pytest tests/

Also the following steps were realized (if applies):

• [x] Check building of documentation with doc/make html