Update (dev) installation documentation

[jwtly10]

Coming from an outside perspective, ran into errors following the readme installation steps. I could look at the code and see why its panicing, but not the best DX.

To reproduce:

1. Fresh repo clone
2. Follow the first installation step https://github.com/BEOpenSourceCollabs/EventManagementCore/blob/685ab6447fd7825adeb126ee74b9db27a3ab3aa5/README.md?plain=1#L19-L35

Added a .env

Huh? Whats SECRET? https://github.com/BEOpenSourceCollabs/EventManagementCore/blob/685ab6447fd7825adeb126ee74b9db27a3ab3aa5/pkg/config/config.go#L40-L54

Oh, JWT secret. Add that.

!!! No mention of setting db url until the next step:

https://github.com/BEOpenSourceCollabs/EventManagementCore/blob/685ab6447fd7825adeb126ee74b9db27a3ab3aa5/README.md?plain=1#L39-L51

Adding the db creds, docker compose up now runs.

Should re-organise the readme so this issue doesnt happen (and perhaps rename the env var SECRET) :)

[jwtly10]

Fixed now