[Doc] Install add a 'Installing with Composer' section
minor #383 [Doc] Install add a 'Installing with Composer' section (nicolas-bastien)

This PR was merged into the master branch.

Discussion
----------

[Doc] Install add a 'Installing with Composer' section

Commits
-------

4779d5d [Doc] Install add a 'Installing with Composer' section
simplified Composer installation docs
made Composer theprimary installation method (instead of PEAR)