Fix page break and header text

[Ugboaja-Uchechi]

What kind of change does this PR introduce?

A bugfix

Issue Number:

Fixes issue #485

Snapshots/Videos:

Before	After

Summary

• In this PR I fixed the page break in the "plugin-architecture" page.
• I also adjusted the font-size of the h2 and h3 tags because of how similar they looked so as to make a clear hierarchy of different headers to make it easier for users to differentiate different headings.

Does this PR introduce a breaking change?

No

Other information

Have you read the contributing guide?

[Cioppolo14]

@Ugboaja-Uchechi Looking at these items, we'd like to close this issue and PR and make a fresh issue that just focuses on the text/heading issue. We'd like to leave the page break issue alone for now.