Fix typo in index.md

What does this MR do?

This MR fixes a typo. Yay!

Does this MR meet the acceptance criteria?

Sorry, I'm not going to read through this for a typo. If this is not the proper way to report a typo, please leave some easy to find information (I DID look for it) on the gitlab homepage. Thanks

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team