Fix grammatical error in README.md

[Sarieme]

Corrected the plural form of 'types' to 'type' for clarity.

Why:

Closes:

What's being changed (if available, include any code snippets, screenshots, or gifs):

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• The changes in this PR meet the docs fundamentals that are required for all content.
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[docs-bot]

👋 Hi there! It looks like you've modified some files that we can't accept as contributions:

• README.md

You'll need to raise a new PR that doesn't include those files, before we can review.

The complete list of files we can't accept are:

• Anything in the root directory
• .devcontainer/**
• .github/**
• data/reusables/rai/**
• src/**
• content/actions/how-tos/secure-your-work/security-harden-deployments/**

We also can't accept contributions to files in the content directory with frontmatter contentType: rai. You can always check out our full contribution guidelines.