Update README.md

[ali-ghazi78]

There was a slash missing in the Readme file. cjson.encode_escape_forward_slash(false)

[doujiang24]

I don't think it needs to change.
In doc, \/ is a plain string, does not need to escape.

[doujiang24]

It just matches the raw result. I don't think it makes people confused.

$ resty -e 'ngx.say(require "cjson" .encode("/"))'
"\/"

[doujiang24]

okay, my mistake.
Markdown render wants to escape too. It renders as the following before the patch.