Enhance readme

[michaelknoch]

Type of change:

Motivation (current vs expected behavior)

• enhance readme, add reference to Ninja and cleanup android steps

Please check if the PR fulfills these requirements

• [ ] Self-review: I am confident this is the simplest and clearest way to achieve the expected behaviour
• [ ] There are no dependencies on other PRs or I have linked dependencies through Zenhub
• [ ] The commit messages are clean and understandable
• [ ] Tests for the changes have been added (for bug fixes / features)

[codecov[bot]]

Codecov Report

Merging #301 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #301   +/-   ##
=======================================
  Coverage   51.97%   51.97%           
=======================================
  Files          87       87           
  Lines        3161     3161           
=======================================
  Hits         1643     1643           
  Misses       1518     1518

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