HADOOP-15184. Add GitHub pull request template. (#1419)

.github/pull_request_template.md

@@ -0,0 +1,6 @@
+## NOTICE
+
+Please create an issue in ASF JIRA before opening a pull request,
+and you need to set the title of the pull request which starts with
+the corresponding JIRA issue number. (e.g. HADOOP-XXXXX. Fix a typo in YYY.)
+For more details, please see https://cwiki.apache.org/confluence/display/HADOOP/How+To+Contribute

pom.xml

@@ -400,6 +400,7 @@ xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/x
             <exclude>.gitattributes</exclude>
             <exclude>.gitignore</exclude>
             <exclude>.git/**</exclude>
+            <exclude>.github/pull_request_template.md</exclude>
             <exclude>.idea/**</exclude>
             <exclude>**/build/**</exclude>
             <exclude>**/patchprocess/**</exclude>