Update signals concept page (open-telemetry#3657)

Author: svrnm

content/en/docs/acknowledgements/_index.md

@@ -16,3 +16,5 @@ this site:
 3. [What is OpenTelemetry - Dynatrace](https://www.dynatrace.com/news/blog/what-is-opentelemetry-2/)
 4. [Understanding OpenTracing, OpenCensus, and OpenMetrics - BMC](https://www.bmc.com/blogs/opentracing-opencensus-openmetrics/)
 5. [Ask Miss O11y: Baggage in OTel - Honeycomb](https://www.honeycomb.io/blog/ask-miss-o11y-opentelemetry-baggage/)
+6. [Observability Whitepaper - CNCF Tag Observability](https://github.com/cncf/tag-observability/blob/whitepaper-v1.0.0/whitepaper.md)
+   for content in [Signals](/docs/concepts/signals/)

content/en/docs/concepts/signals/_index.md

@@ -7,7 +7,20 @@ aliases:
 weight: 11
 ---
 
-In OpenTelemetry, a **[signal][]** refers to a category of telemetry. A brief
-introduction to the currently supported signals is provided in this section.
+The purpose of OpenTelemetry is to collect, process, and export **[signals][]**.
+Signals are system outputs that describe the underlying activity of the
+operating system and applications running on a platform. A signal can be
+something you want to measure at a specific point in time, like temperature or
+memory usage, or an event that goes through the components of your distributed
+system that you'd like to trace. You can group different signals together to
+observe the inner workings of the same piece of technology under different
+angles.
 
-[signal]: /docs/specs/otel/glossary/#signals
+OpenTelemetry currently supports [traces](/docs/concepts/signals/traces),
+[metrics](/docs/concepts/signals/metrics), [logs](/docs/concepts/signals/logs)
+and [baggage](/docs/concepts/signals/baggage). _events_ are a specific type of
+log, and
+[_profiles_ are being worked on](https://github.com/open-telemetry/oteps/blob/main/text/profiles/0212-profiling-vision.md)
+by the Profiling Working Group.
+
+[signals]: /docs/specs/otel/glossary/#signals

content/en/docs/concepts/signals/baggage.md

@@ -1,6 +1,7 @@
 ---
 title: Baggage
 weight: 4
+description: Contextual information that is passed between signals
 ---
 
 In OpenTelemetry, Baggage is contextual information that’s passed between spans.

content/en/docs/concepts/signals/metrics.md

@@ -1,6 +1,7 @@
 ---
 title: Metrics
 weight: 2
+description: A measurement captured at runtime
 ---
 
 A **metric** is a **measurement** of a service captured at runtime. The moment

content/en/docs/concepts/signals/traces.md

@@ -2,6 +2,7 @@
 title: Traces
 weight: 1
 cSpell:ignore: Guten
+description: Understand the full path through your distributed application.
 ---
 
 **Traces** give us the big picture of what happens when a request is made to an