Update docs on error handling output schema.

website/www/site/content/en/documentation/sdks/yaml-errors.md

@@ -37,7 +37,8 @@ The `output` parameter is a name that must referenced as an input to
 another transform that will process the errors (e.g. by writing them out).
 For example,
 the following code will write all "good" processed records to one file and
-any "bad" records to a separate file.
+any "bad" records, along with metadata about what error was encountered,
+to a separate file.
 
 ```
 pipeline:
@@ -77,6 +78,8 @@ for a robust pipeline).
 Note also that the exact format of the error outputs is still being finalized.
 They can be safely printed and written to outputs, but their precise schema
 may change in a future version of Beam and should not yet be depended on.
+Currently it has, at the very least, an `element` field which holds the element
+that caused the error.
 
 Some transforms allow for extra arguments in their error_handling config, e.g.
 for Python functions one can give a `threshold` which limits the relative number