[github]: Add pull request template (#313)

Author: Shuotian Cheng

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,18 @@
+<!--
+Please make sure you have read and understood the contribution guildlines:
+https://github.com/Azure/SONiC/blob/gh-pages/CONTRIBUTING.md
+
+1. Make sure your commit includes a signature generted with `git commit -s`
+2. Make sure your commit title follows the correct format: [component]: description
+3. Make sure your commit message contains enough details about the change and related tests
+
+Please also provide the following information in this pull request:
+-->
+
+**What I did**
+
+**Why I did it**
+
+**How I verified it**
+
+**Details if related**