Add example Mermaid invocation in Wiki documentation

[rnickle]

Thank you for the excellent theme.

Very simply, in the Mermaid section [https://github.com/lxndrblz/anatole/wiki/%F0%9F%93%84-Content-Settings#enabling-the-mermaid-diagram](enabling the mermaid diagraml), add a very simple example invocation such as:

```mermaid
graph TD;
    A-->B;
    A-->C;
    B-->D;
    C-->D;

Also, it seems clear from reading the source and from experimentation that while the Wiki suggests that you must put this block in config.toml, it actually seems to belong in params.toml (or the equivalent params block):

[mermaid]
enable = true

[lxndrblz]

@rnickle Thanks for reaching out. I've updated the relevant section in the wiki:
https://github.com/lxndrblz/anatole/wiki/%F0%9F%93%84-Content-Settings