docs: fix SDK development quickstart

[1amKhush]

Problem

The development quickstart in README.md still refers to the old ContextVM/ts-sdk repository name and uses bun tests, which is not a valid project command.

This is particularly confusing for first-time contributors following the setup instructions verbatim.

Scope

• Change the clone URL to https://github.com/ContextVM/sdk.git.
• Change the checkout directory to sdk.
• Replace bun tests with the repository's supported test command, bun test.
• Check the surrounding development instructions for consistency with package.json and the CI workflows.

Non-goals

• Do not change package scripts or CI behavior.
• Do not change the documented logging API; its current export mismatch needs a separate maintainer decision.

Acceptance criteria

• A newcomer can copy the clone, install, and test commands from the README without correcting them manually.
• The documented commands agree with package.json and .github/workflows/test.yml.
• Markdown renders correctly.

Verification

bun install
bun test