Update README.md with service file info

[kamilsa]

Referenced issues

None

Description of the Change

Adds some information of how to run kagome node using service files

Possible Drawbacks

None

Checklist Before Opening a PR

Before you open a Pull Request (PR), please make sure you've completed the following steps and confirm by answering 'Yes' to each item:

1. Code is formatted: Have you run your code through clang-format to ensure it adheres to the project's coding standards? Yes
2. Code is documented: Have you added comments and documentation to your code according to the guidelines in the project's contributing guidelines? yes
3. Self-review: Have you reviewed your own code to ensure it is free of typos, syntax errors, logical errors, and unresolved TODOs or FIXME without linking to an issue? Yes
4. Zombienet Tests: Have you ensured that the zombienet tests are passing? Zombienet is a network simulation and testing tool used in this project. It's important to ensure that these tests pass to maintain the stability and reliability of the project. Yes