Improved setup instructions in README

[tyearke]

Description

This updates the README file based on feedback from various XDMoD team members.

Motivation and Context

This will make getting started with Open XDMoD easier.

Tests performed

I checked that the new README file renders correctly on GitHub.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project as found in the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[smgallo]

Lets add this to the Contributing section:

If you wish to make contributions to XDMoD you will need to follow these steps:

1. Fork the appropriate XDMoD repos
2. Clone the repos onto your local system
3. Develop and test
4. Commit changes to your fork on Github
5. Initiate a pull request for review by the XDMoD team

A list of supported XDMoD repos can be found at [XDMoD Repo manifest repository][xdmod-repo-manifest].

[smgallo]

And also on the manifest page explicitly list the repos that are part of the XDMoD framework

[jpwhite4]

You need to include instructions about how to install on Centos 6 & 7. This OS has the version of php that doesn't do correct validation of ssl certs. The current instructions to run composer install fail out of the box on both OSes

[jpwhite4]

I did see some warning messages when building the RPMs as per these instructions:

xdmod:

warning: File listed twice: /usr/share/xdmod/html/robots.txt

xdmod-supremm:

[WARN] File not found '/home/jpwhite4/rpmbuild/BUILDROOT/xdmod-supremm-6.0.0-1.0.el6.x86_64/usr/share/xdmod/configuration/linker.php'
[WARN] File not found '/home/jpwhite4/rpmbuild/BUILDROOT/xdmod-supremm-6.0.0-1.0.el6.x86_64/usr/share/xdmod/reporting/jasper_builder/ReportBuilder.sh'
[WARN] File not found '/home/jpwhite4/rpmbuild/BUILDROOT/xdmod-supremm-6.0.0-1.0.el6.x86_64/usr/share/xdmod/configuration/constants.php'
[WARN] File not found '/home/jpwhite4/rpmbuild/BUILDROOT/xdmod-supremm-6.0.0-1.0.el6.x86_64/etc/xdmod/portal_settings.ini'
[WARN] File not found '/home/jpwhite4/rpmbuild/BUILDROOT/xdmod-supremm-6.0.0-1.0.el6.x86_64/usr/local/xdmod/etc/logrotate.d/xdmod'
[WARN] File not found '/home/jpwhite4/rpmbuild/BUILDROOT/xdmod-supremm-6.0.0-1.0.el6.x86_64/etc/cron.d/xdmod'
[WARN] File not found '/home/jpwhite4/rpmbuild/BUILDROOT/xdmod-supremm-6.0.0-1.0.el6.x86_64/usr/local/xdmod/etc/apache.d/xdmod.conf'

Suggest that we add some documentation somewhere that explains these are benign. This should help reduce some support requests.