[glib/wip/antoniof/document_grefstring_type] grefstring: Document GRefString type

[António Fernandes <antoniof src gnome org>]

commit c93430f7951521af0c3b5822b8d0043d1fbe3f18
Author: António Fernandes <antoniojpfernandes gmail com>
Date:   Mon Dec 10 23:01:53 2018 +0000

    grefstring: Document GRefString type
    
    This symbol has been added to glib-sections.txt in 93f3202a615a20cf2f1bc038ad31f98a8c232c5a
    but lacks a gtk-doc comment block.
    
    So, let's add it.

 glib/grefstring.c | 9 +++++++++
 1 file changed, 9 insertions(+)
---
diff --git a/glib/grefstring.c b/glib/grefstring.c
index 56a6181fc..728ebff11 100644
--- a/glib/grefstring.c
+++ b/glib/grefstring.c
@@ -300,3 +300,12 @@ g_ref_string_length (char *str)
 
   return g_atomic_rc_box_get_size (str) - 1;
 }
+
+/**
+ * GRefString:
+ *
+ * A typedef alias for char. This improves readability when passing reference
+ * counted strings and is useful when used together with g_autoptr().
+ *
+ * Since: 2.58
+ */
\ No newline at end of file