Installation guide for rhel8 (likely same for rhel7) missing information on how to properly install rabbitmq and nodejs #997

The installation guide for rhel8 (https://docs.stackstorm.com/install/rhel8.html) is missing information on how to properly install rabbitmq and nodejs v10.

For rabbitmq, need to ensure following yumrepo in place first:
[rabbitmq]
name=rabbitmq
baseurl=https://packagecloud.io/rabbitmq/rabbitmq-server/el/8/x86_64/
enabled=1
....

To properly install st2chatops via "yum install -y st2chatops", we need to issue this command first:
yum module disable -y nodejs

Otherwise rhel8 will complain with following errors:
Error:
Problem: package st2chatops-3.2.0-2.x86_64 requires nodejs >= 2:8.0, but none of the providers can be installed

• conflicting requests
• package nodejs-2:10.21.0-1nodesource.x86_64 is filtered out by modular filtering
• package nodejs-2:10.18.1-1nodesource.x86_64 is filtered out by modular filtering
• package nodejs-2:10.16.3-1nodesource.x86_64 is filtered out by modular filtering
• nothing provides /usr/bin/python needed by nodejs-2:10.16.3-1nodesource.x86_64
• nothing provides python >= 2.6 needed by nodejs-2:10.16.3-1nodesource.x86_64
• package nodejs-2:10.17.0-1nodesource.x86_64 is filtered out by modular filtering
• nothing provides /usr/bin/python needed by nodejs-2:10.17.0-1nodesource.x86_64
• nothing provides python >= 2.6 needed by nodejs-2:10.17.0-1nodesource.x86_64
• package nodejs-2:10.18.0-1nodesource.x86_64 is filtered out by modular filtering
• nothing provides /usr/bin/python needed by nodejs-2:10.18.0-1nodesource.x86_64
• nothing provides python >= 2.6 needed by nodejs-2:10.18.0-1nodesource.x86_64
• package nodejs-2:10.20.0-1nodesource.x86_64 is filtered out by modular filtering
• package nodejs-2:10.20.1-1nodesource.x86_64 is filtered out by modular filtering
• package nodejs-2:10.22.0-1nodesource.x86_64 is filtered out by modular filtering
• package nodejs-2:10.19.0-1nodesource.x86_64 is filtered out by modular filtering
  (try to add '--skip-broken' to skip uninstallable packages or '--nobest' to use not only best candidate packages)