Refactor: Alphabetises OM-terms.md

[darigovresearch]

Description

Alphabetises subsections of OM-terms.md

Would resolve issue #26 if merged

Affected Dependencies

n/a

How has this been tested?

In the browser via GitHub

Checklist

• [x] I have followed the Contribution Guidelines and Code of Conduct
• [x] I have commented my code following the OpenMined Styleguide
• [x] I have labeled this PR with the relevant Type labels
• [x] My changes are covered by tests

[4mber]

Looks great! Thanks! 👍