Judge implementation improvement

Rewritten-docs.md

@@ -2770,23 +2770,40 @@ directory is configurable and can be the same for multiple worker instances.
 
 ### Judges
 
-For future extensibility is critical that judges have some shared interface of
-calling and return values.
+ReCodEx provides a few initial judges programs. They are mostly adopted from
+CodEx system and installed with worker component. Judging programs have to meet
+some requirements. Basic ones are inspired by standard `diff` application -- two
+mandatory positional parameters which have to be the files for comparison and
+exit code reflecting if the results is correct (0) of wrong (1).
+
+This interface lacks support for returning additional data by the judges, for
+example similarity of the two files calculated as Levenshtein's edit distance.
+To allow passing these additional values an extended judge interface can be
+implemented:
 
 - Parameters: There are two mandatory positional parameters which has to be
   files for comparision
 - Results:
     - _comparison OK_
         - exitcode: 0
-        - stdout: there is one line with double value which should be set to 1.0
+		- stdout: there is one line with a double value which should be set to
+		  1.0
     - _comparison BAD_
         - exitcode: 1
-		- stdout: there is one line with double value which should be percentage
-		  of correctness of quality of two given files
+		- stdout: there is one line with a double value which should be
+		  quality percentage of the two given files
 	- _error during execution_
 		- exitcode: 2
 		- stderr: there should be description of error
 
+The additional double value is saved to the results file and can be used for
+score calculation in the frontend. If just the basic judge is used, the values
+are 1.0 for exit code 0 and 0.0 for exit code 1.
+
+If more values are needed for score computation, multiple judges can be used in
+sequence and the values used together. However, extended judge interface should
+comply most of possible use cases.
+
 ### Additional libraries
 
 @todo: libcurl, spdlog, boost, yaml-cpp, libarchive, cppzmq