validator: update readme docs for -s/--schema option

validator/README.md

@@ -1,8 +1,10 @@
 ## OpenTelemetry SDK Configuration Validator
 
-This application will replace environment variables in values of valid yaml files, following the rules of [file configuration environment variable
+This application will replace environment variables in values of valid yaml
+files, following the rules of [file configuration environment variable
 substitution](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/file-configuration.md#environment-variable-substitution),
-before validating that result against the [OpenTelemetry SDK Configuration
+before validating that result against a version of the [OpenTelemetry SDK
+Configuration
 schema](https://github.com/open-telemetry/opentelemetry-configuration/).
 
 ### Build
@@ -21,6 +23,10 @@ Same is true for building the docker image:
 $ make validator-docker
 ```
 
+The schema in the `schema` directory is the default that will be used when
+running the validator. To use a different schema a directory containing the
+schema can be passed with `-s`/`--schema`.
+
 ### Usage
 
 The command `otel_config_validator` takes one argument, the path to the yaml
@@ -49,6 +55,15 @@ Environment variable substitution is supported with the syntax `${VARIABLE}` or
 `${env:VARIABLE}`. Default values are supported in the form
 `${VARIABLE:-default}`.
 
+#### Using a Different Schema Version
+
+To use a version of of the schema other than the one builtin to the
+`otel_config_validator` executable pass the `-s <directory>` option:
+
+```
+$ ./otel_config_validator -o out.json -s .../some/path/opentelemetry-configuration-0.1.0/ ../examples/kitchen-sink.yaml
+```
+
 ### Testing
 
 Run the Go unit tests: