Add jbmc man page

[tautschnig]

This was built using help2man and then manually expanded.

• 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/
• 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

Merging #6972 (f0a410e) into develop (257bfc4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #6972   +/-   ##
========================================
  Coverage    77.83%   77.83%           
========================================
  Files         1571     1571           
  Lines       180484   180484           
========================================
  Hits        140488   140488           
  Misses       39996    39996           

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[peterschrammel]

line 11: This needs to be single-quoted due to the parentheses in the string.