Add a short guide covering common setup and startup pitfalls

[squab-01]

Overview

Running base/node for the first time can be a little tricky if a few setup details are missed. A quick guide highlighting common pitfalls would help new users get up and running faster.
New users may run into basic issues such as missing environment variables, incorrect RPC URLs, or port conflicts. Without clear guidance, they often need to dig through logs or past issues to identify simple mistakes.

Proposed Solution

Add a concise documentation section that lists frequent setup and startup issues along with simple explanations and fixes, written in a friendly and approachable tone.