Fix formatting issues in OpenEXR File Layout Webpage

There are two formatting issues i noticed in the "File Layout" page of openEXR repo.

Fixing these will require basic knowledge of the devops workflow of fork, edit and pull request, and some rudiments of restructed text. These screenshots are taken at [90704f2] on main.

```[tasklist]
### Tasks
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Start with the OpenEXR "File Layout" page as it appeared at commit 90704f2, then locate the source for that webpage and review the three attached screenshots. Correct the two formatting problems shown and verify that the rendered page matches the intended layout.

Written by the indexing model from the issue text.