Update PR template to try and avoid /kind being automatically set

[ghost]

We recently updated the PR template to include some useful examples of
the /kind command. Unfortunately Prow will see those even though they're
inside a comment and apply them to the PR.

This commit removes the valid kind examples and replaces them with some
more text hopefully explaining enough how to use them.

Changes

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes docs (if user facing)
• Commit messages follow commit message best practices
• Release notes block has been filled in or deleted (only if no user facing changes)

See the contribution guide for more details.

Double check this list of stuff that's easy to miss:

• If you are adding a new binary/image to the cmd dir, please update
  the release Task to build and release this image.

Reviewer Notes

If API changes are included, additive changes must be approved by at least two OWNERS and backwards incompatible changes must be approved by more than 50% of the OWNERS, and they must first be added in a backwards compatible way.

Release Notes

NONE

[ghost]

/kind documentation

[vdemeester]

/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vdemeester

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [vdemeester]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[jerop]

/lgtm

[ghost]

/test tekton-pipeline-unit-tests

[ghost]

/test pull-tekton-pipeline-build-tests

[ghost]

/test tekton-pipeline-unit-tests

/test pull-tekton-pipeline-build-tests

[ghost]

# FAILED!
# Cloning tektoncd/pipeline at master(8871a5894ed33d3dd1ca2a6882418d85b5ecbb4a)
# Checking out pulls:
#	3414(d9065a8c2ec0d3ab7ccc7a0ad1b3c592fe105b2b)
$ mkdir -p /home/prow/go/src/github.com/tektoncd/pipeline
$ git init
Initialized empty Git repository in /home/prow/go/src/github.com/tektoncd/pipeline/.git/
$ git config user.name ci-robot
$ git config user.email [email protected]
$ git fetch https://github.com/tektoncd/pipeline.git --tags --prune
fatal: unable to access 'https://github.com/tektoncd/pipeline.git/': Could not resolve host: github.com
# Error: exit status 128

[ghost]

/test tekton-pipeline-unit-tests