Update README

README.md

@@ -111,6 +111,10 @@ second argument and store the result in the third argument
 ### Control Flow
 
 - `jmp` jump to the label given by the first argument
+- `call` put the next statement to execute on the stack and jump to the label
+given by the first argument
+- `ret` pop the the next statement to execute off the stack, e.g. returning to
+the next execution statement before calling `call`
 - `lti` execute next statement if argument 1 is less than argument 2 else skip
 the next statement
 - `gti` execute next statement if argument 1 is greater than argument 2 else
@@ -127,9 +131,11 @@ the first argument
 
 ## Interupts
 
-- [0..9] Output to STDOUT
+- [0..3] Output to STDOUT
 	- `0` put value of register A as ASCII character on stdout
 	- `1` put value of register A as decimal integer on stdout
 	- `2` put value of register A as hexadecimal integer on stdout
 	- `3` put the string pointed at by register A for the amount of characters
-	defined by register B on stdout
+	defined by register B on stdout
+- [4..4] Input from STDIN
+	- `4` get a single ASCII character from STDIN and store it in register A