Auto merge of rust-lang#26032 - achiwhane:master, r=steveklabnik Added a sentence that tells the user that using main.rs and/or lib.rs is required for Cargo.

1.0.0 release 

1.0.0-alpha.2 release 

1.0.0-alpha release 

0.12.0 release 

0.11.0 release 

0.10 release 

0.9 release 

0.8 release