Threads config update in teradata-setup.md (#5973)

## What are you changing in this pull request and why?

Multiple threads are supported by dbt-teradata adapter but the
documentation doesn't mention it.
This can confuse users about whether threads are supported or not.
Made the change that mentions it.

Co-authored-by: Matt Shaver <[email protected]>

website/docs/docs/core/connect-data-platform/teradata-setup.md

@@ -67,7 +67,7 @@ To connect to Teradata Vantage from dbt, you'll need to add a [profile](https://
       password: <password>
       schema: <database-name>
       tmode: ANSI
-      threads: 1
+      threads: [optional, 1 or more]
       #optional fields
       <field-name: <field-value>
 ```