Added pull request template to facilitate standardized contributions. (#779)

Signed-off-by: Leander Stephen D'Souza <leanderdsouza1234@gmail.com>

Author: leander-dsouza

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,18 @@
+<!-- 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 Doc/Nav2 tickets here #1 or N/A) |
+| Does this PR contain AI-generated software? | (No; Yes, and it is marked inline in the code) |
+---
+
+## Description of contribution in a few bullet points
+
+<!--
+* Updated the documentation to reflect corresponding changes in navigation2.
+* Reorganised some sections for better clarity.
+-->