adding PR template (#255)

* adding PR template

* removing empty template fields

* removing awkward HMTL tags for commented examples

.github/PULL_REQUEST_TEMPLATE.md

+<!-- Please fill out the following pull request template for non-trivial changes to help us process your PR faster and more efficiently.-->
+
+---
+
+## Basic Info
+
+| Info | Please fill out this column |
+| ------ | ----------- |
+| Ticket(s) this addresses   | (add tickets here #1) |
+| Primary OS tested on | (Ubuntu, MacOS, Windows) |
+| Primary platform tested on | (Steve's Robot, gazebo simulation of Tally, hardware turtlebot) |
+
+--- 
+
+## Description of contribution in a few bullet points
+
+<!--
+* I added this neat new feature
+* Also fixed a typo in a parameter name in nav2_costmap_2d
+-->
+
+--- 
+
+## Future work that may be required in bullet points
+
+<!--
+* I think there might be some optimizations to be made from STL vector
+* I see alot of redundancy in this package, we might want to add a function `bool XYZ()` to reduce clutter
+* I tested on a differential drive robot, but there might be issues turning near corners on an omnidirectional platform
+-->
+
+---
+
+<!-- OPTIONAL --> 
+
+I'd like to request maintainer: <blank> to review this PR.