Modify Generating Documentation section to use updated instructions for doc generation

Author: nogurenn

docs/docs/contributing/getting-started.md

@@ -83,9 +83,22 @@ Generating Documentation
 -------------------------
 To generate this page and other static page docs, run
 ```bash
+# the generated docs will be located in scaladoc/output
 $ sbt
-> genDocs
+> scalaDoc/generateScalaDocumentation
+
+# or run the following bash script to generate docs under $PWD/docs/_site
+$ ./project/scripts/genDocs
 ```
+See `scaladoc/README.md` for more information on developing with the docs.
+
+To generate docs for a specific module (e.g. `scala3-compiler-bootstrapped`), run
+```bash
+$ sbt
+> scala3-compiler-bootstrapped/doc
+```
+
+
 
 Before contributing to Dotty, we invite you to consult the
 [Dotty Developer Guidelines](https://github.com/lampepfl/dotty/blob/master/CONTRIBUTING.md).