Added comment about hashtable

gmqcc.h

@@ -270,6 +270,13 @@ typedef struct hash_table_t {
 /*
  * hashtable implementation:
  * 
+ * Note:
+ *      This was designed for pointers:  you manage the life of the object yourself
+ *      if you do use this for non-pointers please be warned that the object may not
+ *      be valid if the duration of it exceeds (i.e on stack).  So you need to allocate
+ *      yourself, or put those in global scope to ensure duration is for the whole
+ *      runtime.
+ * 
  * util_htnew(size)                             -- to make a new hashtable
  * util_htset(table, key, value, sizeof(value)) -- to set something in the table
  * util_htget(table, key)                       -- to get something from the table