Updated README with usage notes

README.md

@@ -41,3 +41,32 @@ See the [test plugin base class definition](examples/plugin.h) for an example.
 ## Declaring plugin implementations
 Creating an implementation of a plugin is as simple as inheriting from the plugin base class, and calling the `EXPORT_CLASS_SECTIONED` macro with the correct section
 (or calling a custom export macro defined for the plugin base class, described above). See the [test plugin implementations](examples/plugin_impl.cpp) for an example.
+
+## Usage Notes
+
+### Multiple instances of the same plugin with varying configuration
+
+Objects loaded with `PluginLoader<T>::createInstance` are effectively singleton objects.
+Multiple calls to `PluginLoader<T>::createInstance` with the same arguments will create a pointer to the same object.
+If you need to load multiple instances of the same type of plugin but configured differently, consider making your plugin base class a factory that is itself capable of creating and configuring objects.
+See the [`ShapeFactory` plugin for an example implementation](examples/shape/shape.h).
+
+## Keep plugins in scope during use
+
+Once the plugin object goes out of scope, the library providing it will be unloaded, resulting in undefined behavior and potential segfaults.
+Thus, the plugin object must be kept in scope for as long as it (and objects created by it) are being used.
+Here is an example of what **not** to do:
+
+```c++
+boost_plugin_loader::PluginLoader<ShapeFactory> plugin_loader;
+
+Shape::Ptr shape;
+{
+  ShapeFactory::Ptr square_factory = plugin_loader.createInstance("Square");
+  shape = square_factory.create(2.0);
+
+  // Library providing "Square" plugin is unloaded here when `square_factory` goes out of scope
+}
+
+std::cout << "Square area: " << shape->area() << std::endl;  // <-- segfault because the library providing plugin factory (and the object generated by it) was unloaded
+```