Collator runner instructions

[mrq1911]

new section in hydra docs, similar to the https://docs.hydradx.io/node_setup regarding basic collator setup

if they want to build node from src it has to be from branch hydra-parachain, or they can use latest pre-release with version 12+

bonus

• how to use polkashots to accelerate sync of the relaychain https://polkashots.io/