Update docs/languages/en/ref/installation.rst
Update docs/languages/en/ref/installation.rst

Download links to stable and nightly snapshot needs fixing

Last week I couldn't get the include_path to work with Rob Allens tutorial. Will attempt tutorial later.
gennadiylitvinyuk/zf2-documentation,samsonasik/zf2-documentation,akrabat/zf2-documentation,rettal/zf2-documentation,Rud5G/zf2-documentation,rettal/zf2-documentation,gennadiylitvinyuk/zf2-documentation,samsonasik/zf2-documentation,akrabat/zf2-documentation,Rud5G/zf2-documentation