Document error behavior for Oban.insert_all/3 (#934)

* Document error behavior for Oban.insert_all/3

lib/oban.ex

@@ -419,6 +419,16 @@ defmodule Oban do
   1. This function always returns a list rather than a tuple of `{count, records}`
   2. This function accepts a list of changesets rather than a list of maps or keyword lists
 
+  #### Error Handling and Rollbacks
+  
+  If `insert_all` encounters an issue, the function will raise an error based on your database
+  adapter. This behavior is valuable in conjunction with `c:Ecto.Repo.transaction/2` because it
+  allows for rollbacks.
+  
+  For example, an invalid changeset raises:
+
+  `* (Ecto.InvalidChangesetError) could not perform insert because changeset is invalid.`
+
   > #### 🌟 Unique Jobs and Batching {: .warning}
   >
   > Only the [SmartEngine](https://getoban.pro/docs/pro/smart_engine.html) in [Oban