Explain sign of arg1/arg2

EIPS/eip-145.md

@@ -33,6 +33,8 @@ The `SHL` instruction (shift left) pops 2 values from the stack, `arg1` and `arg
 (arg1 * 2^arg2) mod 2^256
 ```
 
+where both `arg1` and `arg2` are considered as unsigned numbers.
+
 Notes:
 - The shift amount (`arg2`) is interpreted as an unsigned number.
 - If the shift amount (`arg2`) is greater or equal 256 the result is 0.
@@ -45,6 +47,8 @@ The `SHR` instruction (logical shift right) pops 2 values from the stack, `arg1`
 floor(arg1 / 2^arg2)
 ```
 
+Where both `arg1` and `arg2` are considered as unsigned numbers.
+
 Notes:
 - The shift amount (`arg2`) is interpreted as an unsigned number.
 - If the shift amount (`arg2`) is greater or equal 256 the result is 0.
@@ -57,6 +61,8 @@ The `SAR` instruction (arithmetic shift right) pops 2 values from the stack, `ar
 floor(arg1 / 2^arg2)
 ```
 
+where `arg1` is considered as a signed number and `arg2` as an unsigned number.
+
 Notes:
 - The shift amount (`arg2`) is interpreted as an unsigned number.
 - If the shift amount (`arg2`) is greater or equal 256 the result is 0 if `arg1` is non-negative or -1 if `arg1` is negative.