Fixes formatting for the contributing documentation section

[melissawm]

Description

A backtick was missing in one of the "notes" blocks on the Contributing Documentation sections, and this was creating wrong formatting. This is also causing a few anchors in the rendered documentation to not be found, which in turn creates broken links. This can be seen in the "latest" version here: https://napari.org/dev/developers/documentation/index.html

Before:

After:

Type of change

• Fixes or improves existing content
• Adds new content page(s)
• Fixes or improves workflow, documentation build or deployment

References

Final checklist:

• My PR is the minimum possible work for the desired functionality
• I have commented my code, particularly in hard-to-understand areas
• I have added alt text to new images included in this PR

[DragaDoncila]

Thanks @melissawm!