Mention plugin in mise-en-place docs

[EricDriussi]

Hi there!

I'm adding a mention to this plugin in mise docs with this PR.

Just thought I'd mention it over here, of course any improvement suggestion to the setup is more than welcome.

Keep up the good work!

[jmbuhr]

Cool, mise looks useful and I'm glad otter can improve working with it! You may want to only enable otter in mise files and set a keybinding to activate otter for cases where the document doesn't have code when you start editing it and you want to activate otter later after having added code chunks of a new language.