Update issue templates -- delete extra template, add security note (#1003)

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

@@ -1,12 +1,14 @@
 ---
 name: Bug in existing docs
-about: Create a report to help us improve
+about: Report a bug in the documentation
 title: ''
 labels: kind/bug
 assignees: ''
 
 ---
 
+<!-- If you're reporting a bug with Knative itself, open the bug in the corresponding repo. IE., https://github.com/knative/serving for an issue with serving. -->
+<!-- If you need to report a security issue with Knative, send an email to knative-security@googlegroups.com. -->
 ## Expected Behavior
 
 

.github/ISSUE_TEMPLATE/docs-feature-request.md

@@ -6,6 +6,7 @@ labels: ''
 assignees: ''
 
 ---
+
 <!-- For a feature request about a change to Knative, please open the issue in the corresponding repo. -->
 
 **Describe the change you'd like to see**

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

@@ -1,23 +0,0 @@
----
-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