Amazon Linux: Added instructions for installing MongoDB and mongo-cxx-driver to manual installation of dependencies section of README.md

Centos: added build instructions to READMD.md for building mongoDB and mongo-cxx-driver to manual installation of dependencies section for Centos.

Some versions of git do not permit --recurse-submodules on the checkout command so this switches to adding a git submodule update --recursive command instead.  Also cleans up some whitespace to be more consistent.

Signed-off-by: NJoel <you@example.com>

Clarify account.

minor correction in linux build scripts to accomodate small disk sizes that return float when running df -h

added new link to manual dependency install for amazon linux to table of contents, rearranged table of contents in readme.md