Add "readme" documentation to docs.crates.io

[alfiedotwtf]

I can't seem to find any documentation on the "readme" config item in Cargo.toml (which is a link to the file used to display on the crate's page on crates.io)... the only way I found out which setting to add in order to get the README.md to render on my crate's page was to copy what others have done...

This issue is to make this a bit clearer in crates.io's docs.

[stale]

As there hasn't been any activity here in over 6 months I've marked this as stale and if no further activity happens for 7 days I will close it.

I'm a bot so this may be in error! If this issue should remain open, could someone (the author, a team member, or any interested party) please comment to that effect?

The team would be especially grateful if such a comment included details such as:

• Is this still relevant?
• If so, what is blocking it?
• Is it known what could be done to help move this forward?

Thank you for contributing!

(The cargo team is currently evaluating the use of Stale bot, and using #6035 as the tracking issue to gather feedback.)

If you're reading this comment from the distant future, fear not if this was closed automatically. If you believe it's still an issue please leave a comment and a team member can reopen this issue. Opening a new issue is also acceptable!

[ehuss]

This appears to be fixed by #4644.