Add D example. (#303)

README.md

@@ -61,6 +61,7 @@ Every programming language and framework has its own way of caching.
 See [Examples](examples.md) for a list of `actions/cache` implementations for use with:
 
 - [C# - Nuget](./examples.md#c---nuget)
+- [D - DUB](./examples.md#d---dub)
 - [Elixir - Mix](./examples.md#elixir---mix)
 - [Go - Modules](./examples.md#go---modules)
 - [Haskell - Cabal](./examples.md#haskell---cabal)