Merge pull request #152 from buildkite/sup-2200

Update BUILDKITE_MESSAGE explanation in environment_variables.yaml

data/content/environment_variables.yaml

@@ -286,7 +286,7 @@ variables:
       - false
   - name: BUILDKITE_MESSAGE
     desc: |
-      The message associated with the build, usually the commit message. The value is empty when a message is not set. For example, when a user triggers a build from the Buildkite dashboard without entering a message, the variable returns an empty value.
+      The message associated with the build, usually the commit message or the message provided when the build is triggered. The value is empty when a message is not set. For example, when a user triggers a build from the Buildkite dashboard without entering a message, the variable returns an empty value.
     modifiable: false
     example: "Added a great new feature"
   - name: BUILDKITE_ORGANIZATION_ID