[DOC] Move the R examples currently in the README to the HTML documentation

[tbouffard]

Currently (v0.2.2), we have a large amount of information in the README at the project root. Most of them should be centralized in the documentation to avoid duplication and a single source of information.
In addition, the HTML documentation shows the rendered result of the R script so it would provide more details than in a README written in Markdown.

The move can be done once the documentation is publicly available, see #19 and if required, see also #129

https://github.com/process-analytics/bpmn-visualization-R/blob/v0.2.2/README.md?plain=1#L55-L129