Add Compliance.Redaction readme

src/Libraries/Microsoft.Extensions.Compliance.Redaction/README.md

@@ -18,6 +18,42 @@ Or directly in the C# project file:
 </ItemGroup>
 ```
 
+## Usage Example
+
+### Registering the services
+
+The services can be registered using one of the `AddRedaction` overloads:
+
+```csharp
+public static IServiceCollection AddRedaction(this IServiceCollection services);
+public static IServiceCollection AddRedaction(this IServiceCollection services, Action<IRedactionBuilder> configure);
+```
+
+### Configuring a redactor
+
+Redactors can be configured using one of these `IRedactionBuilder` extension methods:
+
+```csharp
+// Sets the redactor to use for a set of data classes.
+IRedactionBuilder SetRedactor<T>(params DataClassificationSet[] classifications);
+
+/// Sets the redactor to use when processing classified data for which no specific redactor has been registered.
+IRedactionBuilder SetFallbackRedactor<T>();
+```
+
+The `ErasingRedactor` is the default fallback redactor. If no redactor is configured for a data classification then the data will be erased.
+
+### Configuring the HMAC redactor
+
+The HMAC redactor can be configured using one these `IRedactionBuilder` extension methods:
+
+```csharp
+public static IRedactionBuilder SetHmacRedactor(this IRedactionBuilder builder, Action<HmacRedactorOptions> configure, params DataClassificationSet[] classifications);
+
+public static IRedactionBuilder SetHmacRedactor(this IRedactionBuilder builder, IConfigurationSection section, params DataClassificationSet[] classifications);
+```
+
+The `HmacRedactorOptions` requires its `KeyId` and `Key` properties to be set.
 
 ## Feedback & Contributing