adding a condition

subjects/concat2args/README.md

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+## concat2args
+
+### Instructions
+
+Write a program that concatenates two arguments and prints the result:
+
+- If the number of arguments is not 2, return a newline.
+- If only one of the arguments is empty, print the other.
+- If the two arguments are empty return a newline.  
+
+### Usage
+
+```console
+$ go run . | cat -e
+$
+$ go run . "Hello" "World!" | cat -e
+HelloWorld!$
+$ go run . "01" "talent" | cat -e
+01talent$
+$ go run . " student " "talented" | cat -e
+ student talented$
+$ go run . "Hello" "student" "talented" "!" | cat -e
+$
+```