[Enhancement]: Add an Example .opf File to the Documentation

[torchyboy]

Describe the feature/enhancement

Add an example .opf file to the documentation section on Additional Metadata. Proposal attached (includes subtitle and asin elements which will be in the next release.

Note: the app supports multiple series / volumeNumber elements, however, when they are read in from a .opf file each one overwrites the previous.

[advplyr]

Is this very large that it needs a zip? Can you put the example OPF text here in the issue?

[torchyboy]

<?xml version='1.0' encoding='utf-8'?>
<ns0:package xmlns:dc='http://purl.org/dc/elements/1.1/' xmlns:ns0='http://www.idpf.org/2007/opf' unique-identifier='BookId' version='2.0'>
  <ns0:metadata xmlns:dc="http://purl.org/dc/elements/1.1/"
          xmlns:opf="http://www.idpf.org/2007/opf">

<!-- Open Packaging Format (opf) File layout for audiobookshelf -->
<!-- author, narrator, genre series, {series/volume number}, and tag can be repeated as desired -->

    <dc:title></dc:title>
    <dc:subtitle></dc:subtitle>
    <dc:description></dc:description>
    <dc:creator opf:role="aut"></dc:creator>      <!-- author -->
    <dc:creator opf:role="nrt"></dc:creator>      <!-- narrator -->
    <dc:publisher></dc:publisher>
    <dc:date></dc:date>                           <!-- publish year -->
    <dc:language>eng</dc:language>
    <dc:subject></dc:subject>                     <!-- genre -->
    <dc:identifier opf:scheme="ISBN"></dc:identifier>
    <dc:identifier opf:scheme="ASIN"></dc:identifier>
    <ns0:meta name="calibre:series" content="" /> <!-- series -->
    <ns0:meta name="calibre:series_index" content="" /> <!-- volumeNumber -->
    <dc:tag></dc:tag>
  </ns0:metadata> 
</ns0:package>

[WirlyWirly]

Thanks for this example, I was scratching my head looking for one. Works great, definitely worth linking to one in the site documentation 👍