Update CONTRIBUTING (#430)

* Fix link for build instructions in CONTRIBUTING

it's not properly generated on GitHub - simple link to a README section,
without rst syntax should work just fine.

* Update link (in CONTRIBUTING.rst) to proper versions file

Ref. #313

Author: lukaszstolarczuk

CONTRIBUTING.rst

@@ -88,7 +88,8 @@ Work with a Local Copy
 ----------------------
 
 For bigger edits you will need a local version of the tools. See
-:ref:`Build the Specification <build_spec>` for instructions.
+`Build the Specification <README.rst#build-the-specification>`_
+for instructions.
 
 -------------
 Editing Tools
@@ -114,7 +115,7 @@ Create a New Version Number
 -----------------------------
 
 Change version in `<oneapi-doc.json>`__ and update the table in
-`<source/versions.rst>`__.
+`<releases/index.rst>`__.
 
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