First usage docs

[bmaher]

Part of #5.

Description

This PR:

• Converts the README to RST
• Documents the basic use-case for Zelt

Types of Changes

What types of changes does your code introduce? Keep the ones that apply:

• Configuration change
• Documentation / non-code

Review

Reviewers' checklist:

• If this PR implements new flows or changes existing ones, are there good tests for these flows? If this PR rather removes flows, are the obsolete tests removed as well?
• Is the documentation still up-to-date and exhaustive? This covers both technical (in source files) and functional (under docs/) documentation.
• Is the changelog updated?
• Does the new version number correspond to the actual changes from this PR? In doubt, refer to https://semver.org.

[zincr[bot]]

🤖 zincr found 0 problems , 1 warning

ℹ️ Large Commits
✅ Approvals
✅ Specification
✅ Dependency Licensing

Details on how to resolve are provided below

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Large Commits

Checks all commits for large additions to a single file. Large commits should be reviewed more carefully for potential copyright and licensing issues

This file contains a substantial change, please review to determine if the change comes from an external source and if there are any copyright or licensing issues to be aware of

• ℹ️ README.md had +100 lines of code changed in a single commit Please review this file to determine the source of this change
• ℹ️ README.rst had +100 lines of code changed in a single commit Please review this file to determine the source of this change
• ℹ️ docs/Run-a-load-test.rst had +100 lines of code changed in a single commit Please review this file to determine the source of this change