Update recog doc and include user-friendly chapter

[AnnaKDS]

I am working on improving the documentation to include a chapter that is particularly directed to people who want to recognise groups with this package and don't have much theoretical background.

It's still WIP but if you have any suggestions, please feel free to comment.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.55%. Comparing base (6d84867) to head (6fe6992).
⚠️ Report is 20 commits behind head on master.

Additional details and impacted files

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- Coverage   78.55%   71.55%   -7.01%     
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  Files          43       43              
  Lines       18281    18398     +117     
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- Hits        14361    13164    -1197     
- Misses       3920     5234    +1314     

see 24 files with indirect coverage changes

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[ThomasBreuer]

some general remarks:

• The introduction distinguishes "naming" and "constructive recognition".
  Can a user ask just for the result of the "naming" phase, or is the result of the user functions always that of the "constructive recognition"? In the latter case, the distinction of the two phases belongs to a more technical part of the manual.
• Chapter "Group recognition" distinguishes a "recognition phase" and a "verification phase".
  What is the status of the results of RecognizeGroup: Is the return value always verified, or may it be incorrect? Asked the other way round: Can one ask for a result without verification?

[fingolfin]

@ThomasBreuer currently verification is not implemented. But it definitely should be made possible for the user to control whether verification happens; and also perhaps certain probabilities.

[frankluebeck]

This is a welcome improvement of the recog documentation.

I have added a few more comments.

After addressing the current comments this should be merged soon. Of course, it can be further improved any time later.

[fingolfin]

I agree with @frankluebeck: I'd rather merge this sooner than later. Even if there are still TODO comment in there. Once it is merged, follow-up PRs can further improve things.