Document --use-base64-encoding for pipectl encrypt

[antedotee]

What happened:
The docs for pipectl encrypt in docs-dev only mention stdin and --input-file, but the CLI supports --use-base64-encoding. Users won’t discover this option from the docs, even though it changes input handling semantics and may be required for certain payloads.

What you expected to happen:
Docs should list --use-base64-encoding as an optional flag for pipectl encrypt, with a short explanation of when to use it.

Evidence:
pipectl encrypt --help shows:

--use-base64-encoding   Whether the plaintext should be base64 encoded before encrypting or not. (default false)

[antedotee]

@eeshaanSA Should I work upon it?

[eeshaanSA]

Thanks, assigned, @antedotee