Fix issues in frontend documentation

[Siena Aguayo]

Describe the bug

• In docs/frontend/installation/README.md, it says "backend" where it should say "frontend," since these are the frontend docs
• The link to the Kubernetes documentation is broken

To Reproduce
Steps to reproduce the behaviour:

1. Navigate to "Badgeyay Frontend" from the main README file
2. Observe it says "backend" where it should say "frontend"
3. Click on "Deployment on Kubernetes"
4. Observe the 404 error from Github

Expected behaviour
The documentation should be clear on whether it refers to the frontend or backend, and the link should be updated to the correct documentation.

Screenshots