Set up issue and PR templates for pkg. (#28)

Fixes: https://github.com/knative/pkg/issues/10

.github/issue-template.md

@@ -0,0 +1,34 @@
+<!--
+Pro-tip: You can leave this block commented, and it still works!
+
+Select the appropriate areas for your issue:
+
+/area API
+/area monitoring
+/area networking
+/area test-and-release
+
+Classify what kind of issue this is:
+
+/kind question
+/kind bug
+/kind cleanup
+/kind doc
+/kind feature
+/kind good-first-issue
+
+-->
+
+## Expected Behavior
+
+
+## Actual Behavior
+
+
+## Steps to Reproduce the Problem
+
+  1.
+  2.
+  3.
+
+## Additional Info

.github/pull-request-template.md

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+<!--
+Pro-tip: To automatically close issues when a PR is merged,
+include the following in your PR description:
+
+Fixes: <LINK TO ISSUE>
+-->