Update contribution.md

Copied the Russian version, since English page had an empty bullet point.

en/contribution.md

@@ -2,9 +2,9 @@
 
 The source files of this document and Diplodoc Platform tools are stored in repositories:
 
-* [Documentation](https://github.com/diplodoc-platform/docs)
-* [Diplodoc](https://github.com/diplodoc-platform/diplodoc)
-* 
+* [Documentation](https://github.com/diplodoc-platform/docs).
+* [Transformer](https://github.com/diplodoc-platform/transform).
+* [Builder](https://github.com/diplodoc-platform/cli).
 
 You can submit bugs and suggestions as GitHub issues in the corresponding repository.