ticloud update should be ticloud upgrade

[pdbossman]

Describe the bug
Incorrect instruction. Instruction says ticloud update - this is not supported syntax. The syntax is ticloud upgrade.

Version (please complete the following information):

• CLI version - ticloud version 1.0.0-beta.11 (build date: 2025-12-23T12:35:25Z commit: b4f1ead)
• OS version - mac os, but irrelevant

To Reproduce
Steps to reproduce the behavior:

1. ticloud update <-- fails.
2. ticloud --help, you'll see ticloud upgrade syntax.

Expected behavior
Just fix the docs. Change update -> upgrade.