docs: add pagination instructions

Author: jaredcnance

README.md

@@ -151,3 +151,13 @@ You can add a namespace to the URL by specifying it in `ConfigureServices`:
 services.AddJsonApi<AppDbContext>(
     opt => opt.Namespace = "api/v1");
 ```
+
+## Pagination
+
+If you would like pagination implemented by default, you can specify the page size
+when setting up the services:
+
+```
+ services.AddJsonApi<AppDbContext>(
+     opt => opt.DefaultPageSize = 10);
+```