Created SC2131 (markdown)

SC2131.md

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+## This format string has 2 variables, but is passed 1 arguments.
+
+### Problematic code:
+
+```sh
+printf "Hello %s, welcome to %s.\n" "$USER"
+```
+
+### Correct code:
+
+```sh
+printf "Hello %s, welcome to %s.\n" "$USER" "$HOSTNAME"
+```
+### Rationale:
+
+ShellCheck has noticed that you're using a `printf` format string with more `%s` variables than arguments to fill them.
+
+In the problematic example case, the last `%s` will just become an empty string each time.
+
+You should either remove the unused variables from the format string, or add enough arguments to fill them.
+
+### Exceptions:
+
+None.