chore: Add pull request template (#100)

## What issue does this PR close?

Doesn't close an issue in the tracker. PR messages should match the
structure of
commits in this repo and other arrow projects.

## What's Changed

Adds a PR template for better consistency. Based on
apache/arrow-swift#19 and
https://github.com/apache/arrow-js/blob/main/.github/pull_request_template.md.

---------

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

Author: Benjamin-Philip

.github/pull_request_template.md

@@ -0,0 +1,28 @@
+<!--
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements.  See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership.  The ASF licenses this file
+  to you 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.
+-->
+
+## What issue does this PR close?
+
+Closes #NNN.
+
+## What's Changed
+
+Please fill in a description of the changes here.
+
+**This contains breaking changes.** <- Remove this line if there are no breaking changes.