Linux Expand Firewalld Documentation

[DaintyJet]

We should expand the firewalld Documentation. Although we should be using iptables (nftables) to keep everything uniform, it does not hurt to have more though documentation on firewalld for future people.

What is Firewalld.
What is the model it uses for filtering packets. (IPTables is a series of tables and chains which the packet is compared against in a specific order).
How can you add rules to block or allow traffic based on the destination or source?
How can you add rules to allow traffic if it has already been established (Outbound allowed back in)?
How can you integrate this with container networking like Docker.

Scripts to setup and configure.