Added NoSQL callout (#343)

episodes/00-sql-introduction.md

@@ -181,9 +181,28 @@ To summarize:
   containing parts we might want to work with separately.
 - One field per type of information
 - No redundant information
-  - Split into separate tables with one table per class of information
-  - Needs an identifier in common between tables – a shared column - to
-    reconnect the information (known as a *foreign key* constraint).
+- Split into separate tables with one table per class of information
+- Needs an identifier in common between tables – a shared column - to
+ reconnect data (known as a *foreign key*).
+
+:::::::::::::::::::::::::::::::::::::::::  callout
+
+### SQL vs. NoSQL
+
+SQL is not the only tool for managing and analyzing large amounts of data.
+As described above, SQL databases store data in tables using a rigid schema.
+This works well for many applications, but larger, more complex projects may
+benefit from the more flexible approach provided by NoSQL databases. A common application for NoSQL databases is storing documents and files.
+
+NoSQL databases are diverse, employing a variety of data structures tailored
+to specific use cases, but in general provide a scalable way to store, search,
+and establish relationships within large datasets that cannot easily be
+represented by a rigid, tabular schema.
+A more thorough discussion of the differences between SQL and NoSQL
+is beyond the scope of this lesson, but curious readers can start with
+[this comparison](https://www.mongodb.com/nosql-explained/nosql-vs-sql) by MongoDB, a NoSQL database vendor.
+
+::::::::::::::::::::::::::::::::::::::::::::::::::
 
 ### Import