Installation instructions `eval "$(phpenv init -)"` isn't explicit in the install file

[christianchristensen]

In https://github.com/CHH/phpenv/blob/master/bin/phpenv-install.sh#L84 when installing I added what the output on the screen mentioned, but I had to then look at the README.md to see the proper line to add to my ~/.bashrc (and worked). This should be the same instructions...