Error message is misleading when config file is not present

[zealsham]

When you run payjoin-cli , it checks for the presence of a config file in the current directory . However , if that file isn't present , the error message displayed does not tell exactly what went wrong .

//misleading error message 
Error: Valid V2 configuration is required for BIP77 mode: missing field `ohttp_relays`

For such cases , we should tell the user that a config file is missing and if #64 goes in , we can tell the user to add a config file in the .payjoin directory .

[spacebear21]

A config file isn't strictly necessary since individual parameters can be specified as cli arguments (e.g. --ohttp_relays=https://pj.bobspacebkk.com), but perhaps the error message could clarify this.