[docs] custom command documentation has wrong file redirect

I found a bug in the docs for claude-code on the page https://docs.anthropic.com/en/docs/agents-and-tools/claude-code/tutorials#use-claude-as-a-unix-style-utility
$ claude > /user:security-review
Should be
$ claude < /user:security-review
in order to read in the command rather than overwrite it.