Add pull request template

Author: Jake Hageman

.github/pull_request_template.md

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+**Describe the contribution**
+A clear and concise description of what the contribution is [e.g. Fixes issue #X]
+
+**Testing performed**
+Steps taken to test the contribution:
+1. Build steps '...'
+2. Execution steps '....'
+
+**Expected behavior changes**
+A clear and concise description of how this contribution will change behavior and level of impact.
+ - API Change: xxx (if applicable)
+ - Behavior Change: xxx (if applicable)
+ - Or no impact to behavior
+
+**System(s) tested on:**
+ - Hardware
+ - OS: [e.g. Linux 4.4]
+ - Versions [e.g. cFE 6.6, OSAL 4.2, PSP 1.3 for mcp750, any related apps]
+
+**Additional context**
+Add any other context about the contribution here.
+
+**Contributor Info**
+Full name and company/organization of all contributors (required for acceptance)
+
+**Community contributors**
+You must attach a signed CLA (required for acceptance) or reference one already submitted