Add Github pull request template

Add Github pull request template

Author: silabs-DanielN

.github/pull_request_template.md

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+<!-- Comment:
+A great PR typically begins with the lines below.
+Please note that:
+- The contents of this comment block are not shown in the pull request body.
+- Once a new pull request is opened in the project 
+or new commit to an existing pull request will start a new build 
+to automatically update the status of every commit on every branch. 
+Read https://confluence.silabs.com/display/SCLP/GitHub+Pull+Request+Jenkins for more.
+- To disable the PR bot, keyword [NOCHECKS] should be added to the PR description.
+-->
+
+**[Description]**
+Hi There,
+This is a short description of a pull request.
+It can be multiline with empty lines as well.
+
+**[Files]**
+- inc/driver.h
+- src/driver.c
+- test/app.c
+- etc.
+
+**[Video]**
+- https://www.dropbox.com/s/xly3vc68dvkj2rt/pull_request_template.mp4?dl=0