Document metadata mapping

* Add notes on metadata mapping to README.md
* Alphabetize fields in crossref.py

https://mitlibraries.atlassian.net/browse/DLSPP-82

README.md

@@ -1,2 +1,21 @@
 # wiley-deposits
 Wiley Deposits
+
+
+### Crossref to Dublin Core metadata mapping
+
+Crossref field|DC field|Field notes
+------ | ------ | -------
+author|dc.contributor.author|Multiple values possible, create separate field instances for each value. Names concatenated as Family, Given. "
+issued|dc.date.issued|
+ISSN|dc.identifier.issn|Multiple values possible, create separate field instances for each value.
+language|dc.langauge|
+publisher|dc.publisher|
+URL|dc.relation.isversionof|
+container-title|dc.relation.journal|
+title|dc.title|
+original-title|dc.title.alternative|
+subtitle|dc.title.alternative|
+short-title|dc.title.alternative|
+issue|mit.journal.issue|
+volume|mit.journal.volume|

awd/crossref.py

@@ -22,20 +22,20 @@ def get_crossref_work_from_doi(api_url, doi):
 def get_metadata_dict_from_crossref_work(work):
     """Create metadata dict from a Crossref work JSON record."""
     keys_for_dspace = [
-        "publisher",
-        "issue",
-        "page",
-        "title",
-        "volume",
         "author",
         "container-title",
-        "original-title",
+        "ISSN",
+        "issued",
+        "issue",
         "language",
-        "subtitle",
+        "original-title",
+        "page",
+        "publisher",
         "short-title",
-        "issued",
+        "subtitle",
+        "title",
         "URL",
-        "ISSN",
+        "volume",
     ]
     work = work["message"]
     value_dict = {}