JOSS review - Figure 2 contrast

[pabloitu]

This issue tracks a comment by @sscivier from the JOSS review thread.

Source (JOSS): openjournals/joss-reviews#9408 (comment)

A quick note on Fig 2 of the paper. I think it works well to have an example config.yml file. However, there is not sufficient contrast between the text and background colours, which makes it difficult to read.

[pabloitu]

Updated figure 2 contrast with different colors for the background and text to improve visibility. Changes added in #108

[pabloitu]

Closed with #108