chore: Update README .NET repo link

[hjgraca]

Why is this needed?

Readme .NET link is pointing to the docs instead of the repo like other languages.

Which area does this relate to?

Other

Solution

Update .net project readme hyperlink

Acknowledgment

• This request meets Powertools for AWS Lambda (Python) Tenets
• Should this be considered in other Powertools for AWS Lambda languages? i.e. Java, TypeScript, and .NET

[boring-cyborg]

Thanks for opening your first issue here! We'll come back to you as soon as we can.
In the meantime, check out the #python channel on our Powertools for AWS Lambda Discord: Invite link

[github-actions]

This is now released under 2.18.0 version!