Update GDExtension tutorial for entry functions

Docs part of godotengine/godot-cpp#1095
Same changes as godotengine/godot-cpp#1115

Author: paddy-exe

tutorials/scripting/gdextension/gdextension_cpp_example.rst

@@ -268,8 +268,8 @@ GDExtension plugin.
 
     extern "C" {
     // Initialization.
-    GDExtensionBool GDE_EXPORT example_library_init(const GDExtensionInterface *p_interface, const GDExtensionClassLibraryPtr p_library, GDExtensionInitialization *r_initialization) {
-        godot::GDExtensionBinding::InitObject init_obj(p_interface, p_library, r_initialization);
+    GDExtensionBool GDE_EXPORT example_library_init(GDExtensionInterfaceGetProcAddress p_get_proc_address, const GDExtensionClassLibraryPtr p_library, GDExtensionInitialization *r_initialization) {
+        godot::GDExtensionBinding::InitObject init_obj(p_get_proc_address, p_library, r_initialization);
 
         init_obj.register_initializer(initialize_example_module);
         init_obj.register_terminator(uninitialize_example_module);
@@ -348,6 +348,7 @@ loaded for each platform and the entry function for the module. It is called ``g
     [configuration]
 
     entry_symbol = "example_library_init"
+    compatibility_minimum = 4.1
 
     [libraries]
 
@@ -369,6 +370,8 @@ loaded for each platform and the entry function for the module. It is called ``g
     android.release.arm64 = "res://bin/libgdexample.android.template_release.arm64.so"
 
 This file contains a ``configuration`` section that controls the entry function of the module.
+You are also able to set a minimum compatible version with ``compatability_minimum`` of Godot
+which prevents older version of Godot to load your extension.
 
 The ``libraries`` section is the important bit: it tells Godot the location of the
 dynamic library in the project's filesystem for each supported platform. It will