Edit new troubleshooting doc

doc/administration/troubleshooting/elasticsearch.md

@@ -5,7 +5,7 @@ Troubleshooting ElasticSearch requires:
 - Knowledge of common terms.
 - Establishing within which category the problem fits.
 
-## Common Terminology
+## Common terminology
 
 - **Lucene**: A full-text search library written in Java.
 - **Near Realtime (NRT)**: Refers to the slight latency from the time to index a
@@ -138,7 +138,7 @@ graph TD;
   F7(Escalate to<br>GitLab support.)
 ```
 
-## Troubleshooting Walkthrough
+## Troubleshooting walkthrough
 
 Most ElasticSearch troubleshooting can be broken down into 4 categories:
 
@@ -317,7 +317,7 @@ dig further into these.
 Feel free to reach out to GitLab support, but this is likely to be something a skilled
 ElasticSearch admin has more experience with.
 
-## Common Issues
+## Common issues
 
 All common issues [should be documented](../../integration/elasticsearch.md#troubleshooting). If not,
 feel free to update that page with issues you encounter and solutions.