subject(swapName):add readme

subjects/swapname/README.md

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+## swap-name
+
+### Instructions
+
+Write a program that takes two words in the first argument and swaps them.
+- If the number of arguments is not 2, nothing should be printed.
+- If the first argument is not a string, the program should print `"Error\n"`.
+- Skip the spaces in the first of the two words.
+- Print the result with a new line at the end (`'\n'`).
+
+### Usage
+
+```console
+$ go run . | cat -e
+$ go run . "Hello World" "Hello World" | cat -e
+$ go run . "Hello World" | cat -e
+World Hello$
+$ go run . "He2 $%hello" | cat -e
+Error$
+$ go run . "   Hello World" | cat -e
+World Hello$
+$ go run . "Hello World   " | cat -e
+Error$
+$ go run . "Hello World Hello" | cat -e
+Error$
+```