Update Onix example file & Add codelist for mapping (#70)

* Update Onix

* Fix style

---------

Co-authored-by: Robert Organ <robert.organ@schibsted.com>

Author: pj-gitlab-bot

docs/feeds/product/formats/onix/onix.md

@@ -7,6 +7,8 @@ title: 'Onix For Books XML'
 
 If your products are books, we support the [Onix For Books](https://www.editeur.org/14/Code-Lists/) XML format to import your products.
 
+Code list for mappings can be found [here](https://www.editeur.org/files/ONIX%20for%20books%20-%20code%20lists/ONIX_BookProduct_Codelists_Issue_65.html).
+
 ## Example Files
 
 ```xml
@@ -37,6 +39,7 @@ If your products are books, we support the [Onix For Books](https://www.editeur.
     <DescriptiveDetail>
       <ProductComposition>00</ProductComposition>
       <ProductForm>00</ProductForm>
+      <ProductFormDetail>E116</ProductFormDetail>
       <ProductFormDescription>CD-skiva</ProductFormDescription>
       <Measure>
         <MeasureType>01</MeasureType>
@@ -82,6 +85,18 @@ If your products are books, we support the [Onix For Books](https://www.editeur.
         <SubjectSchemeIdentifier>95</SubjectSchemeIdentifier>
         <SubjectCode>2ACB</SubjectCode>
       </Subject>
+      <Extent>
+          <ExtentType>00</ExtentType>
+          <ExtentValue>200</ExtentValue>
+          <ExtentUnit>03</ExtentUnit>
+      </Extent>
+      <Contributor>
+          <SequenceNumber>2</SequenceNumber>
+          <ContributorRole>A01</ContributorRole>
+          <PersonNameInverted>King, Ben</PersonNameInverted>
+          <NamesBeforeKey>Ben</NamesBeforeKey>
+          <KeyNames>King</KeyNames>
+      </Contributor>
     </DescriptiveDetail>
     <CollateralDetail/>
     <PublishingDetail>
@@ -145,4 +160,4 @@ If your products are books, we support the [Onix For Books](https://www.editeur.
     </ProductSupply>
   </Product>
 </ONIXMessage>
-```
+```