fix broken formatting of resp body and headers in the example of readme.md
fix broken formatting of resp body and headers in the example of readme.md

Frederick888/curl-rust,svmk/curl-rust,compressed/curl-rust,alexcrichton/curl-rust,carllerche/curl-rust,alexcrichton/curl-rust,alexcrichton/curl-rust,posix4e/curl-rust,zetok/curl-rust