docs: add no-TEE swtpm development guide

[kvinwang]

Summary

• document how to build and identify a development guest image
• show how to run dstack with --no-tee and key_provider=tpm
• document encrypted-disk and restart-persistence verification
• add the guide to the root README

Validation

Tested end-to-end on Ubuntu 24.04 with KVM, QEMU 8.2.2, and swtpm 0.7.3:

• development TEE simulator reached Boot Progress: done
• VMM launched QEMU together with swtpm
• guest reported encryption=true, filesystem=Zfs
• guest opened /dev/mapper/dstack_data_disk using the detached LUKS2 header
• after a graceful stop/start, the instance ID remained unchanged
• the second boot mounted the existing data disk and started the existing container

git diff --check passes.

[Copilot]

Pull request overview

This PR adds documentation for developing and testing dstack on machines without TEE hardware by using --no-tee plus swtpm for persistent TPM-backed keys, and links the new guide from the root README.

Changes:

• Add a new end-to-end guide for building a development guest image and running the VMM in no-TEE mode with swtpm persistence checks.
• Document an optional nested-KVM (libvirt) lab setup for Ubuntu 24.04.
• Link the new guide from README.md for discoverability.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
README.md	Adds a top-level link to the new no-TEE + swtpm development guide.
docs/development-without-tee.md	New guide covering build, setup, launch, and persistence verification in no-TEE mode.

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