Update QuickStart section in README with library registration instruc…

…tions

The README.md has been updated to include instructions on how to register the library with the dependency injection container at startup before generating a PDF document from the template. This ensures the correct use of the `Generator` class.

README.md

@@ -70,7 +70,15 @@ Next, create an XML template. Here is a simple example:
 </template>
 ```
 
-Now, you can use the `Generator` class to generate a PDF document from the template:
+After registering the library with your dependency injection container at startup:
+
+```csharp
+// ...
+services.AddPdfTemplateServices();
+// ...
+```
+
+You can use the following code to generate a PDF document from the template:
 
 ```csharp
 // IServiceProvider serviceProvider