Improve readability of the documentation

See gh-41051

Author: mateusscheper

spring-boot-project/spring-boot-docs/src/docs/asciidoc/actuator/observability.adoc

@@ -1,7 +1,7 @@
 [[actuator.observability]]
 == Observability
 Observability is the ability to observe the internal state of a running system from the outside.
-It consists of the three pillars logging, metrics and traces.
+It consists of the three pillars: logging, metrics and traces.
 
 For metrics and traces, Spring Boot uses https://micrometer.io/docs/observation[Micrometer Observation].
 To create your own observations (which will lead to metrics and traces), you can inject an `ObservationRegistry`.