Update docs

src/OpenTelemetry.Exporter.Jaeger/README.md

@@ -29,24 +29,39 @@ dotnet add package OpenTelemetry.Exporter.Jaeger
 ## Configuration
 
 You can configure the `JaegerExporter` through `JaegerExporterOptions`
+and environment variables. The `JaegerExporterOptions` setters
+take precedence over the environment variables.
+
+## Options Properties
+
+The `JaegerExporter` can be configuring using the `JaegerExporterOptions`
 properties:
 
-* `AgentHost`: Usually `localhost` since an agent should usually be running on
-  the same machine as your application or service.
-* `AgentPort`: The compact thrift protocol port of the Jaeger Agent (default
-  `6831`).
+* `AgentHost`: The Jaeger Agent host (default `localhost`).
+* `AgentPort`: The compact thrift protocol UDP port of the Jaeger Agent
+  (default `6831`).
 * `MaxPayloadSizeInBytes`: The maximum size of each UDP packet that gets
-  sent to the agent. (default `4096`).
+  sent to the agent (default `4096`).
 * `ExportProcessorType`: Whether the exporter should use
   [Batch or Simple exporting processor](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk.md#built-in-span-processors)
-  .
+  (default `ExportProcessorType.Batch`).
 * `BatchExportProcessorOptions`: Configuration options for the batch exporter.
   Only used if ExportProcessorType is set to Batch.
 
 See the
 [`TestJaegerExporter.cs`](../../examples/Console/TestJaegerExporter.cs)
 for an example of how to use the exporter.
 
+## Environment Variables
+
+The following environment variables can be used to override the default
+values of the `JaegerExporterOptions`.
+
+| Environment variable              | `JaegerExporterOptions` property |
+| --------------------------------- | -------------------------------- |
+| `OTEL_EXPORTER_JAEGER_AGENT_HOST` | `AgentHost`                      |
+| `OTEL_EXPORTER_JAEGER_AGENT_PORT` | `AgentPort`                      |
+
 ## References
 
 * [Jaeger](https://www.jaegertracing.io)