Update specification with in memory collections documentation

docs/usage/use-specification-inmemory-collection.md

@@ -7,6 +7,54 @@ nav_order: 4
 
 # How to use Specifications with In Memory Collections
 
-You can use Specifications on collections of objects in memory.
+You can use Specifications on collections of objects in memory. This approach can be convenient when retrieving data doesn't require querying a remote or out of process data store like a database. If the process does require querying external persistence, it is better to refer to the practices for using a Specification with a [Repository Pattern](./use-specification-repository-pattern.md) or [DbContext](./use-specification-dbcontext.md).
 
-(todo)
+A Specification can be applied to an in memory collection using the `Evaluate` method. This method takes a single parameter of type `IEnumerable<T>` representing the collection on which the underlying query expression will be appled to. In this example, the `GetEnvironment` method of the `Example` class handles creating a Specification and applying it to the collect static collection of Environment entities.
+
+```csharp
+public class Environment
+{
+    public string Name { get; set; }
+    public string Description { get; set; }
+}
+
+public class EnvironmentByNameSpec : Specification<Environment>
+{
+    public EnvironmentByNameSpec(string name)
+    {
+        Query.Where(h => h.Name == name);
+    }
+}
+
+public static class Example
+{
+    private static readonly Environment[] Environments = new Environment[]
+    {
+        new()
+        {
+            Name = "DEV",
+            Description = "this application's development environment"
+        },
+        new()
+        {
+            Name = "QA",
+            Description = "this application's QA environment"
+        },
+        new()
+        {
+            Name = "PROD",
+            Description = "this application's production environment"
+        }
+    };
+
+    public static Environment GetEnvironment(string name)
+    {
+        var specification = new EnvironmentByNameSpec(name);
+
+        var environment = specification.Evaluate(Environments)
+            .Single();
+
+        return environment;
+    }
+}
+```