patch 8.2.1961: various comments can be improved

Problem:    Various comments can be improved.
Solution:   Various comment adjustments.
diff --git a/src/dict.c b/src/dict.c
index 8d07644..b3ef35a 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -22,6 +22,7 @@
 
 /*
  * Allocate an empty header for a dictionary.
+ * Caller should take care of the reference count.
  */
     dict_T *
 dict_alloc(void)