doc: add note about call to "regfree" after call to "string_regcomp" (plugin API reference)

src/core/wee-string.c

@@ -1300,6 +1300,8 @@ string_regex_flags (const char *regex, int default_flags, int *flags)
  * Returns:
  *   0: successful compilation
  *   other value: compilation failed
+ *
+ * Note: regex must be freed with regfree after use.
  */
 
 int