pub fn content_type(mut self, mime_type: &str) -> Self {
        self.headers.insert(
            header::CONTENT_TYPE,
            HeaderValue::from_str(mime_type).unwrap(),
        );
        self
    }
Sets the `Content-Type` HTTP header to the given MIME type, which tells
the browser what file type it has actually been given. For HTML, this is
especially important!

As this is typically called last, and only once, it consumes `self` for
ergonomics. If this is not desired, the `.add_header()` method can
be manually invoked.

# Panics

This will panic if the given MIME type contains invalid ASCII
characters.
packages/perseus/src/turbine/server.rs