Man pages: improve wording of unwinding-related options

[tautschnig]

man-page contents for options controlling loop unwinding was particularly terse, with the statement for "partial-loops" not actually helping readers. This is an attempt to remain succinct while still providing meaningful insight.

• 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.
• 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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.22%. Comparing base (a209b44) to head (36ba12e).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8471   +/-   ##
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  Coverage    78.22%   78.22%           
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  Files         1726     1726           
  Lines       189038   189038           
  Branches     18265    18265           
========================================
  Hits        147874   147874           
  Misses       41164    41164           

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[kroening]

Most people don't know the word "unsound" -- I'd say "may result in false alarms".

[tautschnig]

Most people don't know the word "unsound" -- I'd say "may result in false alarms".

Indeed, reworded.