Fix typo in the AddSubmission script

[MaGaroo]

Edit help message of the --contest-id argument

The name of the script is "Add Submission" but there is "id of contest where to add the user" in the help message. So I thought that would've been a mistake.

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This change is 

[codecov]

Codecov Report

Merging #1178 (9a1ff46) into master (ed4e05f) will increase coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1178      +/-   ##
==========================================
+ Coverage   63.44%   63.61%   +0.17%     
==========================================
  Files         232      232              
  Lines       17046    17046              
==========================================
+ Hits        10815    10844      +29     
+ Misses       6231     6202      -29     

Flag	Coverage Δ
functionaltests	47.63% <ø> (+0.15%)	⬆️
unittests	44.05% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmscontrib/AddSubmission.py	73.73% <ø> (ø)
cms/service/ScoringService.py	68.18% <0.00%> (-1.52%)	⬇️
cms/io/service.py	71.51% <0.00%> (-1.22%)	⬇️
cms/service/ResourceService.py	59.11% <0.00%> (-0.89%)	⬇️
cms/db/fsobject.py	75.75% <0.00%> (-0.76%)	⬇️
cms/db/submission.py	97.93% <0.00%> (-0.52%)	⬇️
cms/grading/Job.py	88.83% <0.00%> (-0.45%)	⬇️
cms/io/rpc.py	94.21% <0.00%> (ø)
cms/server/admin/handlers/base.py	69.63% <0.00%> (ø)
cms/server/contest/handlers/contest.py	87.37% <0.00%> (+0.97%)	⬆️
... and 5 more

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[andreyv]

Thanks, indeed this looks like a mistake. Merging.