chore: add notice to CHANGELOG.md regarding feature #103

CHANGELOG.md

@@ -6,6 +6,7 @@
 ### Features
 
 * add new Firestore.runAsyncTransaction ([#103](https://www.github.com/googleapis/java-firestore/issues/103)) ([b28b660](https://www.github.com/googleapis/java-firestore/commit/b28b66088194f997cca62f759e4201cba3da38b5))
+  * __NOTICE__ This change will require any users of the library that implement `com.google.cloud.firestore.Firestore` to have to implement the new runAsyncTransaction methods, and is a binary incompatible change in Java 7. Those users who only use `com.google.cloud.firestore.Firestore` through the instance returned from `FirestoreOptions.getDefaultInstance().getService()` will not have to recompile their code.
 * add Query.limitToLast() ([#151](https://www.github.com/googleapis/java-firestore/issues/151)) ([c104615](https://www.github.com/googleapis/java-firestore/commit/c104615210271977a48205a8d8e6acd69acc5fb6))
 * base transaction retries on error codes ([#129](https://www.github.com/googleapis/java-firestore/issues/129)) ([00b6eb3](https://www.github.com/googleapis/java-firestore/commit/00b6eb3703c8f4942d6da42b827ecbeeb9a13ef5)), closes [googleapis/nodejs-firestore#953](https://www.github.com/googleapis/nodejs-firestore/issues/953)
 * use SecureRandom instead of Random to reduce the chance of auto-id collisions ([#156](https://www.github.com/googleapis/java-firestore/issues/156)) ([0088ee7](https://www.github.com/googleapis/java-firestore/commit/0088ee7b1f0c5bb65d7636de77e2c7f9098978e9))