Updated readme: added REPL and errors examples

README.md

@@ -1,15 +1,31 @@
 # Reverse Polish notation calculator in .NET C#
 
-Pass RPN expression as one string as an argument.
+Pass RPN expression as one string as an argument or run without arguments for REPL. Calculator also has basic error handler. 
 
-## Example
+## Examples
+
+### Argument expression example
 
 ```powershell
 dotnet run "5 3 +"
-# >> 8
+8
 
 dotnet run "10 2 - 5 +"
-# >> 13
+13
 ```
 
-P.S.I still hate OOP, so code is rather imperative
+### REPL examples
+
+```powershell
+dotnet run
+>> 5 3 +
+8
+>> 10 2 a +
+... 2 a + 
+      ^ got unknown operator
+>> 10 2 - * 5 + 
+... 2 - * 5 + ...
+        ^ operator requires 2 arguments
+```
+
+P.S.I still hate OOP (don't know it well), so code improvements are welcomed