add missing word to title (#6679)

Author: alexravenna

content/en/docs/concepts/distributions.md

@@ -1,7 +1,7 @@
 ---
 title: Distributions
 description: >-
-  A distribution, not to be confused with a fork, is customized version of an
+  A distribution, not to be confused with a fork, is a customized version of an
   OpenTelemetry component.
 weight: 190
 ---