[gimp] libgimp: add some comment documentation to Gimp*Proc callback types.

[Jehan <jehanp src gnome org>]

commit 692272e580b76c318d2205492507e282a0ee3ac0
Author: Jehan <jehan girinstud io>
Date:   Thu Jul 25 11:24:40 2019 +0200

    libgimp: add some comment documentation to Gimp*Proc callback types.
    
    It doesn't really help yet with the problem I encountered allowing to
    set and run these Python callbacks from the C code (cf. pygobject#347),
    but at least let's improve a bit the documentation.

 libgimp/gimp.h | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
---
diff --git a/libgimp/gimp.h b/libgimp/gimp.h
index e0273d1f04..13df071e67 100644
--- a/libgimp/gimp.h
+++ b/libgimp/gimp.h
@@ -68,9 +68,36 @@ G_BEGIN_DECLS
 #define gimp_set_data         gimp_procedural_db_set_data
 
 
+/**
+ * GimpInitProc:
+ *
+ * The init procedure is run at every GIMP startup.
+ */
 typedef void (* GimpInitProc)  (void);
+/**
+ * GimpQuitProc:
+ *
+ * The quit procedure is run when GIMP closes.
+ */
 typedef void (* GimpQuitProc)  (void);
+/**
+ * GimpQueryProc:
+ *
+ * The initialization procedure is run at GIMP startup, only the first
+ * time after a plug-in is installed, or if it has been updated.
+ */
 typedef void (* GimpQueryProc) (void);
+/**
+ * GimpRunProc:
+ * @name: the name of the procedure which has been called.
+ * @n_params: the number of parameters passed to the procedure.
+ * @param: (array length=n_params): the parameters passed to @name.
+ * @n_return_vals: the number of values returned by @name.
+ * @return_vals: (array length=n_return_vals): the returned values.
+ *
+ * The run procedure is run during the lifetime of the GIMP session,
+ * each time a plug-in procedure is called.
+ */
 typedef void (* GimpRunProc)   (const gchar      *name,
                                 gint              n_params,
                                 const GimpParam  *param,