doc: add controller env variable examples

[saumeya]

Signed-off-by: saumeya [email protected]

What type of PR is this?

/kind documentation

What does this PR do / why we need it:

Have you updated the necessary documentation?

• [x] Documentation update is required by this PR.
• [x] Documentation has been updated.

Which issue(s) this PR fixes:

Fixes #?

How to test changes / Special notes to the reviewer: