Update issue templates (knative#643)

.github/ISSUE_TEMPLATE/bug-in-existing-docs.md

@@ -0,0 +1,28 @@
+---
+name: Bug in existing docs
+about: Create a report to help us improve
+title: ''
+labels: kind/bug
+assignees: ''
+
+---
+
+## Expected Behavior
+
+
+## Actual Behavior
+
+
+## Steps to Reproduce the Problem
+
+1.
+1.
+1.
+
+## Additional Info
+**Additional context**
+Add any other context about the problem here.
+
+**Install information:**
+ - Platform (GKE, IKS, AKS, etc.):
+ - Knative Version:

.github/ISSUE_TEMPLATE/feature-request----new-or-updated-documentation.md

@@ -0,0 +1,23 @@
+---
+name: Feature request -- new or updated documentation
+about: For upcoming changes to the documentation
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+## What is changing? (Please include as many details as possible.)
+
+## How will this impact our users?
+
+## When will the change take effect (to the best of your knowledge)?
+
+## Context
+Link to associated PRs or issues from other repos here.
+
+1.
+1.
+1.
+
+## Additional info