Add note about Runtime.start() blocking behavior in Getting Started docs

[coderabbitai]

Description

The Getting Started documentation should include a note about the blocking behavior of Runtime.start() to prevent confusion for users in interactive environments like Jupyter notebooks or Python REPLs.

Current Issue

The current documentation shows:

Runtime(
    namespace="MyProject",
    name="DataProcessor", 
    nodes=[SampleNode]
).start()

However, .start() blocks the main thread, which can be problematic in interactive environments.

Suggested Improvement

Add a short note explaining the blocking behavior and provide alternative patterns for interactive environments, such as:

• Running the runtime in a background thread
• Using asyncio patterns (e.g., asyncio.to_thread)
• Mentioning any non-blocking/async API alternatives if available

Location

File: docs/docs/exosphere/getting-started.md around lines 81-87

Backlinks

• PR: Documentation update #279
• Comment: Documentation update #279 (comment)
• Requested by: @NiveditJain