DEV-3386 docs(onlyb):add subject

subjects/onlyb/README.md

@@ -0,0 +1,16 @@
+## only-b
+
+### Instructions
+
+Write a program that displays a `b` character on the standard output. (and nothing else)
+
+### Usage
+
+```console
+$ go run .
+b
+$ go run . "a" "b"
+b
+$ go run . "a" "b" "c"
+b
+```