docs: add some more docs

doc/tutorial2.md

@@ -0,0 +1,67 @@
+# Tutorial 2
+
+In this tutorial we show how to connect to a PipeWire daemon and 
+enumerate the objects that it has.
+
+## Initialization
+
+Let take a look at the following application to start.
+
+```c
+#include <pipewire/pipewire.h>
+
+static void registry_event_global(void *data, uint32_t id,
+		uint32_t permissions, const char *type, uint32_t version,
+		const struct spa_dict *props)
+{
+	printf("object: id:%u type:%s/%d\n", id, type, version);
+}
+
+static const struct pw_registry_events registry_events = {
+	PW_VERSION_REGISTRY_EVENTS,
+	.global = registry_event_global,
+};
+
+int main(int argc, char *argv[])                                                
+{                                                                               
+        struct pw_main_loop *loop;                                              
+        struct pw_context *context;                                             
+        struct pw_core *core;                                                   
+        struct pw_registry *registry;                                           
+        struct spa_hook registry_listener;                                      
+                                                                                
+        pw_init(&argc, &argv);                                                  
+                                                                                
+        loop = pw_main_loop_new(NULL /* properties */);                         
+        context = pw_context_new(pw_main_loop_get_loop(loop),                   
+                        NULL /* properties */,                                  
+                        0 /* user_data size */);                                
+                                                                                
+        core = pw_context_connect(context,                                      
+                        NULL /* properties */,                                  
+                        0 /* user_data size */);                                
+                                                                                
+        registry = pw_core_get_registry(core, PW_VERSION_REGISTRY,              
+                        0 /* user_data size */);                                
+                                                                                
+        spa_zero(registry_listener);                                            
+        pw_registry_add_listener(registry, &registry_listener,                  
+                                       &registry_events, NULL);                 
+                                                                                
+        pw_main_loop_run(loop);                                                 
+                                                                                
+        pw_proxy_destroy((struct pw_proxy*)registry);                           
+        pw_core_disconnect(core);                                               
+        pw_context_destroy(context);                                            
+        pw_main_loop_destroy(loop);                                             
+                                                                                
+        return 0;                                                               
+}                                  
+```
+
+To compile the simple test application, copy it into a test2.c file and
+use:
+
+```
+gcc -Wall test2.c -o test2 $(pkg-config --cflags --libs libpipewire-0.3)
+```