Merge pull request #4075 from newrelic/4048-syntax

fix(TDP): clarify when to include backticks

src/content/docs/telemetry-data-platform/custom-data/custom-events/data-requirements-limits-custom-event-data.mdx

@@ -104,6 +104,8 @@ When reporting custom events and attributes, follow these general requirements f
 
         Event types (using the `eventType` attribute) can be a combination of alphanumeric characters, colons (`:`), and underscores (`_`).
 
+        If the name begins with anything other than an alphabetical character, enclose the name with backticks.
+
         Do not use [words reserved for use by NRQL](#reserved-words).
       </td>
     </tr>