[CONTRIBUTING] add trivial change clause

[macfarla]

PR description

Adds a clause covering trivial changes. We've seen an increase in this type of PR lately (typos, punctuation, and other trivial changes). These add load to CI and also to reviewers. Until now we did not have a policy on these types of PRs.

These words came from Teku

Please keep in mind that we do not accept non-code contributions like fixing comments, typos or some other trivial fixes. Although we appreciate the extra help, managing lots of these small contributions is unfeasible, and puts extra pressure in our continuous delivery systems (running all tests, etc). Feel free to open an issue pointing any of those errors, and we will batch them into a single change.

Fixed Issue(s)

Thanks for sending a pull request! Have you done the following?

• Checked out our contribution guidelines?
• Considered documentation and added the doc-change-required label to this PR if updates are required.
• Considered the changelog and included an update if required.
• For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• unit tests: ./gradlew build
• acceptance tests: ./gradlew acceptanceTest
• integration tests: ./gradlew integrationTest
• reference tests: ./gradlew ethereum:referenceTests:referenceTests

[siladu]

If you add a header section, you should be able to link directly to it.

[siladu]

LGTM, linkable header section would be a minor improvement

[lu-pinto]

Even though there's some helpful comment fixes it can be a bit of a gray area what to and what not to allow, so I think not allowing them altogether is what makes most sense from the POV of time/resources wasted with little benefit.
The approach to just create issues for typos is a good one IMO.

[garyschulte]

🚢