Fix format of nondet volatile command line help

[danpoe]

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• n/a Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[peterschrammel]

⛏️ would be good if the help text didn't exceed 80 chars.

[danpoe]

Ok, added a function help_entry() which automatically wraps the text at 80 chars.

[codecov]

Codecov Report

Merging #5379 into develop will increase coverage by 0.01%.
The diff coverage is 97.05%.

@@             Coverage Diff             @@
##           develop    #5379      +/-   ##
===========================================
+ Coverage    68.17%   68.18%   +0.01%     
===========================================
  Files         1173     1173              
  Lines        97461    97494      +33     
===========================================
+ Hits         66445    66478      +33     
  Misses       31016    31016              

Flag	Coverage Δ
#cproversmt2	42.45% <0.00%> (-0.03%)	⬇️
#regression	65.36% <0.00%> (-0.03%)	⬇️
#unit	32.21% <100.00%> (+0.02%)	⬆️

Impacted Files	Coverage Δ
.../goto-instrument/goto_instrument_parse_options.cpp	58.48% <0.00%> (ø)
src/util/parse_options.h	100.00% <ø> (ø)
src/util/string_utils.h	100.00% <ø> (ø)
src/util/parse_options.cpp	77.46% <100.00%> (+8.83%)	⬆️
src/util/string_utils.cpp	92.00% <100.00%> (+1.67%)	⬆️

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