docs: Move the GFileMonitor SECTION

Move it to the struct docs.

Signed-off-by: Philip Withnall <philip@tecnocode.co.uk>

Helps: #3037

gio/gfilemonitor.h

@@ -41,11 +41,6 @@ G_BEGIN_DECLS
 typedef struct _GFileMonitorClass       GFileMonitorClass;
 typedef struct _GFileMonitorPrivate	GFileMonitorPrivate;
 
-/**
- * GFileMonitor:
- *
- * Watches for changes to a file.
- **/
 struct _GFileMonitor
 {
   GObject parent_instance;