feat: add new exam exercise

subjects/front-back/README.md

@@ -0,0 +1,26 @@
+## front-back
+
+## front-back
+
+- Write a program that prints the previous and next alphabet of a given alphabet.
+    - If the number of arguments is different from `1`, print `"\n"`.
+    - If the length of the argument is different from `1`, print `"\n"`
+    - If the argument is not a letter, print `"\n"`
+    - Print the previous alphabet and the next alphabet except for the last alphabet of the alphabet.
+
+### Usage
+
+```shell
+$ go run . | cat -e 
+$
+$ go run . a | cat -e
+ab$
+$ go run . "B" | cat -e
+ABC$
+$ go run . "z" | cat -e
+yz$
+$ go run . "Hello World!" | cat -e
+$
+$ go run . "1" | cat -e
+$
+```