Say that storage is not transactional

Part of #267

lang/spec.html

@@ -8580,12 +8580,12 @@ <h4>Retry statement</h4>
 <h3 id="transactions">Transactions</h3>
 
 <p>
-Ballerina supports distributed transactions. A global transaction consists of
-multiple transaction branches, where a branch corresponds to work done by a
-single strand of a Ballerina program that is part of the global transaction.
-Every transaction branch is uniquely identified by an XID, which consists of an
-identifier of the global transaction and an identifier of a branch with the
-global transaction.
+Ballerina provides language support for distributed transactions. A global
+transaction consists of one or more transaction branches, where a branch
+corresponds to work done by a single strand of a Ballerina program that is part
+of the global transaction. Every transaction branch is uniquely identified by an
+XID, which consists of an identifier of the global transaction and an identifier
+of a branch with the global transaction.
 </p>
 <p>
 At runtime, there is a mapping from each strand to a transaction stack, which is
@@ -8606,6 +8606,12 @@ <h3 id="transactions">Transactions</h3>
 belongs.
 </p>
 <p>
+Note that internal storage in Ballerina is not transactional. Rolling back a
+transaction does <em>not</em> automatically restore the mutable values are
+variables to their state when the transaction started. It is up to the
+programmer to do this using commit or rollback handlers.
+</p>
+<p>
 Static checking is based on the idea of a transactional scope: this is a lexical
 region of the program where it is known that at runtime the strand executing the
 region will always be in transactional mode. A function with the