DOSCP-34797: Clarify key definition

Author: norareidy

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+    "esbonio.sphinx.confDir": ""
+}

source/source-connector/fundamentals/specify-schema.txt

@@ -25,9 +25,9 @@ sent to Apache Kafka.
 
 .. important:: Note on Terminology
 
-   The word "key" has a slightly different meaning in the context
-   of BSON and Apache Kafka. In BSON, a "key" is a unique string identifier for
-   a field in a document.
+   This guide uses the Apache Kafka definition of the word "key", which differs
+   slightly from the BSON definition. In BSON, a "key" is a unique string identifier
+   for a field in a document.
 
    In Apache Kafka, a "key" is a byte array sent in a message used to determine
    what partition of a topic to write the message to. Kafka keys can be