Add missing reserved CloudKit keywords (#255)

* Add missing reserved CloudKit keywords

We missed a couple.

* Clarify note on reserved CloudKit fields

Updated the note about reserved CloudKit fields to clarify that an exhaustive list has not been published by Apple.

Author: stephencelis

Sources/SQLiteData/Documentation.docc/Articles/CloudKit.md

@@ -289,15 +289,18 @@ In the process of sending data from your database to CloudKit, the library turns
 internally by CloudKit and are reserved for their use only. This means those keys cannot be used
 as field names in your Swift data types or SQLite tables.
 
-Here is an exhaustive list of those reserved fields:
+While Apple has not published an exhaustive list of reserved keywords, the following should cover
+most known cases:
 
-* `recordID`
-* `recordType`
 * `creationDate`
 * `creatorUserRecordID`
-* `modificationDate`
+* `etag`
 * `lastModifiedUserRecordID`
+* `modificationDate`
+* `modifiedByDevice`
 * `recordChangeTag`
+* `recordID`
+* `recordType`
 
 ## Backwards compatible migrations