Add cache-control headers for readme files.

[smarnach]

We added cache-control headers for .crate files in #1871. We should also add cache-control headers for readme files. While it is rare, readme files can change when we regenerate them, so we can't mark them as immutable, and should limit the cache time to some lower value, say one week.

[hbina]

So I assume

crates.io/src/uploaders.rs

Lines 90 to 97 in 1ccd730

	pub fn upload<R: std::io::Read + Send + 'static>(
	&self,
	client: &reqwest::Client,
	path: &str,
	mut content: R,
	content_length: u64,
	content_type: &str,
	extra_headers: Option<header::HeaderMap>,

should no longer wraps extra_headers in Option<T>?

[rye]

Do I have it right that #1924 resolved this?

[smarnach]

@rye Yes, this is fixed now.