docs: Add readme for subject concatenate

subjects/concatenate/README.md

@@ -0,0 +1,14 @@
+## concatenate
+
+### Instructions
+
+Write a program that displays all the arguments as a single string. If there are not enough arguments it should display a new line.
+
+### Usage
+
+```console
+$ go run . hello there chris | cat -e
+hellotherechris$
+$ go run . a b c d| cat -e
+abcd$
+```