[documentation] end user documentation needs to be updated for the upcoming mainnet release

There are 3 main documents that needs updates:

Since older releases may be required for future releases, its released with the same release tag as that of the Peerplays mainnet and is available here https://github.com/PBSA/peerplays-infrastructure-docs/releases/tag/1.5.16

Documentation for the new version will be available in the master branch of the git repository and thus will get published under Peerplays.tech