docs: Move mdoc sources to just example/mdoc

Author: jakubjanecek

CONTRIBUTING.md

@@ -33,7 +33,7 @@ sbt fix
 
 ## Documentation
 
-The project contains [compiled documentation](https://scalameta.org/mdoc) which is located in [example/src/main/mdoc](example/src/main/mdoc).
+The project contains [compiled documentation](https://scalameta.org/mdoc) which is located in [example/mdoc](example/mdoc).
 Please do update it with your changes and recompile it to check that everything is fine using the following command:
 
 ```bash

build.sbt

@@ -70,7 +70,7 @@ lazy val example = project
     publish / skip := true,
     run / fork := true,
     Global / cancelable := true,
-    mdocIn := baseDirectory.value / "src" / "main" / "mdoc",
+    mdocIn := baseDirectory.value / "mdoc",
     mdocOut := baseDirectory.value / ".." / "docs",
     libraryDependencies += Dependencies.logbackClassic
   )