Documentation link incorrect

[Michael Owen]

Not sure if this is the best place to post this, but as I was looking through the following page:

• https://protobuf.dev/programming-guides/dos-donts/ I noticed that the link for the '1-1-1-Rule', as highlighted in the attached image, is wrong.  

It currently points to: 

• https://protobuf.dev/programming-guides/1-1-1.md

And I think it should point to: 

• https://protobuf.dev/programming-guides/1-1-1/

[Daz Wilkin]

https://github.com/protocolbuffers/protocolbuffers.github.io/pull/177