Clarify usage of INC/DEC on only integer quantities.

Author: dmsc

manual.md

@@ -1623,6 +1623,9 @@ General Statements
   equivalent to "_var_ = _var_ - 1",
   but faster.
 
+  _var_ can be any integer variable or
+  integer array element.
+
 
 **Allocate An Array**  
 **DIM _arr_(_size_) [type], .../ DI.**
@@ -1670,6 +1673,9 @@ General Statements
   equivalent to "_var_ = _var_ + 1",
   but faster.
 
+  _var_ can be any integer variable or
+  integer array element.
+
 
 **Pauses Execution**  
 **PAUSE _num_ / PA.**