change usage and rewrite subjects

subjects/swapname/README.md

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+## swap-name
+
+### Instructions
+
+Write a program that takes a first and last name as one argument and swaps them.
+- If there is more than one argument, nothing should be printed.
+- The argument should contain only alphabetic characters and spaces and only two words, if not, you have to print `"Error\n"`
+- The result must be followed with a new line at the end (`'\n'`).
+- Trim any extra space in the beginning or end of the string.
+
+### Usage
+
+```console
+$ go run . | cat -e
+$ go run . "James Carl" "Peter Lab" | cat -e
+$ go run . "ROB carlos" | cat -e
+carlos ROB$
+$ go run . "He2 $%hello" | cat -e
+Error$
+$ go run . "    JULIE BIRD   " | cat -e
+BIRD JULIE$
+$ go run . "Carl Jon Mic" | cat -e
+Error$
+$ go run . "ROB" | cat -e
+Error$
+```