doc: add CONFIGURATION.md

[cameri]

Description

1. Document the environment variables and settings file

Related Issue

#19

Motivation and Context

Without proper documentation, someone looking to run nostr-ts-relay would need to look in the code to understand what the different environment variables and settings are and their purpose.

How Has This Been Tested?

Testing not needed.

Screenshots (if appropriate):

Types of changes

• Non-functional change (docs, style, minor refactor)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• All new and existing tests passed.

[coveralls]

Pull Request Test Coverage Report for Build 3325726496

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 70.588%

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Totals
Change from base Build 3309014838:	0.0%
Covered Lines:	466
Relevant Lines:	685

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💛 - Coveralls