Add more description to journal_file field

[alexesmet]

The issue is that journal_file init option purpose may be confusing for some users. For example, they may think they need to specify a file for logging, like in journalctl.

Only after hours of debugging your code I was able to find out that it expects me to specify path to .beancount file.

[mmoya]

Somehow related to #48.

[polarmutex]

Latest version should not require setting the journal file and just operate on the current file by default

My next focus is documentation and testing when I can find time to work on it

[francocalvo]

How is this currently working? I've pointed the journal file to my main.bean file, which imports various files (accounts, commodities, etc) and the journals for each year. Currently, this is throwing an error, and the workaround is importing the accounts, etc to the journal too.

[polarmutex]

the journal file should parse that file and any include statements in each file parsed

could you provide more detail or a small example to help debug this issue?