docs: add package-info to jdbc (#264)

* docs: add package-info to jdbc

Adds a package-info.java file to the com.google.cloud.spanner.jdbc package, with
a simple example for how to create a JDBC connection.

* fix: run linter

src/main/java/com/google/cloud/spanner/jdbc/package-info.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2020 Google LLC
+ *
+ * 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.
+ */
+
+/**
+ * A JDBC driver for Cloud Spanner - A no-compromise relational database service.
+ *
+ * <p>Example for creating a JDBC connection to Cloud Spanner.
+ *
+ * <pre>{@code
+ * String projectId = "my-project";
+ * String instanceId = "my-instance";
+ * String databaseId = "my-database";
+ *
+ * try (Connection connection =
+ *     DriverManager.getConnection(
+ *         String.format(
+ *             "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
+ *             projectId, instanceId, databaseId))) {
+ *   try (Statement statement = connection.createStatement()) {
+ *     try (ResultSet rs = statement.executeQuery("SELECT CURRENT_TIMESTAMP()")) {
+ *       while (rs.next()) {
+ *         System.out.printf(
+ *             "Connected to Cloud Spanner at [%s]%n", rs.getTimestamp(1).toString());
+ *       }
+ *     }
+ *   }
+ * }
+ * }</pre>
+ *
+ * @see <a
+ *     href="https://googleapis.dev/java/google-cloud-spanner-jdbc/latest/com/google/cloud/spanner/jdbc/JdbcDriver.html">JdbcDriver
+ *     java doc</a> for all supported connection URL properties.
+ * @see <a href="https://cloud.google.com/spanner/docs/use-oss-jdbc">Cloud Spanner JDBC Driver</a>
+ */
+package com.google.cloud.spanner.jdbc;