amend contributing guide to ban trivial contributions (#15618)

Signed-off-by: deepthi <deepthi@planetscale.com>

CONTRIBUTING.md

@@ -15,3 +15,7 @@ to let everyone know what you're planning to work on, and to track progress and
 * How to make yourself familiar with Go and Vitess.
 * How to go through the GitHub workflow.
 * What to look for during code reviews.
+
+### Contributions Related to Spelling and Grammar
+
+At this time, we will not be accepting contributions that only fix spelling, naming or grammatical errors in documentation, code, comments or elsewhere, from accounts created in the last 365 days. We appreciate your interest in contributing to Vitess, and we encourage you to contribute in other ways.