Documentation suggestion: edit and modify, relevance of -a option for changes to fields in path

Since I use `$year` in my `paths:` rules in config, I was wondering why my files paths did not get updated after making changes to the `year` field. Bug? Well, no, I finally realised that my queries lacked the `-a` option, so I was editing the `year` field of individual tracks, while the `year` field that is used by the `paths:` rules is actually the `year` field of the album object. This is a subtle difference that can be misunderstood by the novice user.

So, I suggest the following addition to the documentation of the `modify` command and of the `edit` plugin: the paragraph that documents the `-a` option could be extended with something like the following:

Using the `-a` option allows you to make changes to album fields, instead of track fields. This is relevant if you are using the `year` field in your paths format configuration [link to config.html#path-format-configuration]: if you need to make changes to that field, make sure to use the `-a` option in your query; in this way, you will be changing the album's `year` field (not the tracks one), and the new value will be used to also update the path in the library and on the filesystem.