[llvm] [docs] Replace llvm.org/docs links with project links (PR #222506)

[Petr Hosek via llvm-commits]

================
@@ -10,7 +10,7 @@
 ## Description
 
 Utility for displaying information from, and converting between different
-[remark](https://llvm.org/docs/Remarks.html) formats.
+{doc}`remark <../Remarks>` formats.
----------------
petrhosek wrote:

For document references the following should work and is idiomatic Markdown.
```suggestion
[remark](../Remarks.md) formats.
```

https://github.com/llvm/llvm-project/pull/222506