docs: add beginner Quickstart example to Blob README

[alymkarim]

This adds a minimal working example to help new users test connection, upload a file, and list blobs.

Description

This pull request adds a beginner-friendly Quickstart example to the azure-storage-blob README.

It provides a minimal Python script that:

• Connects to Azure Blob Storage using a connection string
• Creates a container if it doesn't exist
• Uploads a local file (example.txt)
• Lists all blobs in the container

The goal is to help students, analysts, and first-time Azure developers quickly validate their setup before using more advanced features.

No SDK code changes were made — this is documentation only.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message.

[github-actions]

Thank you for your contribution @alymkarim! We will review the pull request and get back to you soon.

[alymkarim]

@microsoft-github-policy-service agree

[jalauzon-msft]

Hi @alymkarim, thanks for your contribution! While this is useful information to have, I believe everything you have included in the README already exists in one place or another. The prerequisites and install command can be found earlier in the README and the samples can all be found in our samples directory along with many other samples.

While I do see the value in having it in one place like you have done, I don't think we should be duplicating this information and additionally, having more complex samples in the README can be difficult to maintain as the code evolves. Samples in the samples directory run in our test pipelines are therefore regularly verified.