fix(doc): make installation from git work again (#570)
fix(doc): make installation from git work again (#570)

cargo install --git https://github.com/rust-lang-nursery/mdBook.git
leads to error: multiple packages with binaries found: mdbook, mdbook-wordcount
Fix: append name of binary (`mdbook`).
azerupi/mdBook,azerupi/mdBook,azerupi/mdBook,azerupi/mdBook