[Salesforce action] Add faq regarding undefined traits error

Added the following in FAQ section
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"Why do I see undefined traits error?

When using the `update` operation, this error will occur if no value is past in the field that is set as Record Matcher. Please check that you have provided a value in the field that is set as the Record Matcher."

Author: tanjinhong72

src/connections/destinations/catalog/actions-salesforce/index.md

@@ -159,6 +159,10 @@ When using the `create` operation, it's possible for duplicate records to be cre
 
 Please note this is only a concern when using the `create` operation. You can use the `upsert` operation instead to avoid duplicates if `upsert` meets your needs.
 
+## Why do I see undefined traits error?
+
+When using the `update` operation, this error will occur if no value is past in the field that is set as Record Matcher. Please check that you have provided a value in the field that is set as the Record Matcher.
+
 ### How does Salesforce Bulk API work?
 When **Use Salesforce Bulk API** is enabled for your mapping, events are sent to [Salesforce’s Bulk API 2.0](https://developer.salesforce.com/docs/atlas.en-us.api_asynch.meta/api_asynch/asynch_api_intro.htm){:target="_blank"} rather than their streaming REST API. If enabled, Segment will collect events into batches of up to 5000 before sending to Salesforce. Bulk support can be used for the `upsert` or `update` operations only.