Add jdiff 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 #6971 (a445cd7) into develop (de250f9) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #6971   +/-   ##
========================================
  Coverage    77.87%   77.87%           
========================================
  Files         1569     1569           
  Lines       180903   180903           
========================================
  Hits        140882   140882           
  Misses       40021    40021           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a96dea4...a445cd7. Read the comment docs.

[peterschrammel]

⛏️ --cover* options should probably read as "add instrumentation for creating test-suite..." resp. "add instrumentation in order not to stop..."