translate `clean-data.Rmd`, `validate.Rmd`, `describe-cases.Rmd`

[avallecam]

• https://epiverse-trace.github.io/tutorials-early/clean-data.html
• https://epiverse-trace.github.io/tutorials-early/validate.html
• https://epiverse-trace.github.io/tutorials-early/describe-cases.html