some more info

README.md

@@ -27,12 +27,17 @@ standard input.
 * ability to enter integer commands (positive and negative) into program memory;
 * ability to enter floating (or fixed) point numbers (positive and negative) at
   program runtime;
+* the lowest data memory size is 128 cells (126 of which are mutable);
+* the highest data memory size is 16384 cells (16382 of which are mutable);
+* the lowest program memory size is 128 steps (127 of which are mutable);
+* the highest program memory size is 16384 steps (16383 of which are mutable);
 * immutability of the data address 0 (must always return 0 when accessed);
-* immutability of the data address 127 (must always return 1 when accessed).
+* immutability of the data address 127 (must always return 1 when accessed);
+* immutability of the instruction number 0 (reserved for immediate execution).
 
 The following things are implementation-dependent:
 
-* instruction and data internal representation;
+* instruction and data internal representation and capacity;
 * tracing capabilities;
 * runlimit (the amount of program steps before forcefully halting the program).
 
@@ -257,7 +262,9 @@ and the above mnemonics (case-insensitive). The recommended file suffix is
 An assembly line looks like this (the optional parts are enclosed in square
 brackets): `[:lbl] MNEMONIC arg1 arg2 arg3 [;comment]`. Labels are optional but
 must start with a colon (`:`) and be on the same line before the instruction
-they label. The mnemonics are specified above in the core opcode list.
+they label. The mnemonics are specified above in the core opcode list and the
+shortcut list. In the second case, shortcuts accept less instruction parameters
+than the opcode they refer to.
 
 Here, the exact assembly algorithm is specified step-by-step for each line in
 the MU8A assembly file to convert it into a plain text based machine code