Document that Scrypt is used by default

Author: rachelmyers

src/main/java/com/google/firebase/auth/hash/Scrypt.java

@@ -26,7 +26,7 @@
  * Represents the Scrypt password hashing algorithm. This is the
  * <a href="https://github.com/firebase/scrypt">modified Scrypt algorithm</a> used by
  * Firebase Auth. See {@link StandardScrypt} for the standard Scrypt algorithm. Can be used as an
- * instance of {@link com.google.firebase.auth.UserImportHash} when importing users.
+ * instance of {@link com.google.firebase.auth.UserImportHash} when importing users. This is the default algorithm for passwords.
  */
 public final class Scrypt extends RepeatableHash {
 

src/main/java/com/google/firebase/auth/hash/package-info.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2021 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.auth.hash;
+
+/**
+ * By default, passwords are stored as Scrypt hashes. The hashing algorithm used to store passwords can be changed to any supported algorithm by changing the project config via the API or by <href="https://firebase.google.com/docs/auth/admin/import-users">reimporting</href> existing users.
+ */