Add release instructions

[remyroy]

Part of #26 . Also fixes #26

Changes

• Document the release process with step by step instructions for anyone to be able to release a new version of ethstaker-deposit-cli.

Types of changes

What types of changes does your code introduce?

• Bugfix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (a change that causes existing functionality not to work as expected)
• Optimization
• Refactoring
• Documentation update
• Build-related changes
• Other: Description

Testing

Requires testing

• Yes
• No

If yes, did you write tests?

• Yes
• No

Notes on testing

This will be tested with the next test release to be created in the new few days.

Documentation

Requires documentation update

• Yes
• No

This is the documentation update.

Requires explanation in Release Notes

• Yes
• No

This is mostly internal documentation.