Deleted trailing space in hello-cargo.md
Added note about build --release in hello-cargo
thanks to steven klabnik for pointing it out for me
edited out redundant wording
This commit is an attempt to standardize the use of punctuation and
formatting in "The Rust Programming Language" as discussed in #19823.
- Convert bold text to italicized textcwhen referring to terminology.
- Convert single-quoted text to italicized or double-quoted text,
depending on context.
- Use double quotes only in the case of scare quotes or quotations.
