Switch relative link refs to absolute

PyPI doesn't support github relative link refs and breaks the rendering of the package description.

Author: int3l

README.rst

@@ -82,9 +82,8 @@ Add the following config, if you have tessdata error like: "Error opening data f
 
 * **nice** Integer, modifies the processor priority for the Tesseract run. Not supported on Windows. Nice adjusts the niceness of unix-like processes.
 
-* **output_type** Class attribute, specifies the type of the output, defaults to ``string``. For the full list of all supported types, please check the definition of `pytesseract.Output`_ class.
+* **output_type** Class attribute, specifies the type of the output, defaults to ``string``. For the full list of all supported types, please check the definition of `pytesseract.Output <https://github.com/madmaze/pytesseract/blob/master/src/pytesseract.py>`_ class.
 
-.. _pytesseract.Output: src/pytesseract.py
 
 INSTALLATION
 ------------