Fix the markdown syntax in the folder walkthrough doc

[NlightNFotis]

This allows for prettier rendering in the docs website.

Fixes #7397

• Each commit message has a non-empty body, explaining why the change was made.
• 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/
• 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).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Base: 78.37% // Head: 78.38% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (0841040) compared to base (941030e).
Patch coverage: 94.26% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #7399   +/-   ##
========================================
  Coverage    78.37%   78.38%           
========================================
  Files         1647     1647           
  Lines       190328   190362   +34     
========================================
+ Hits        149172   149213   +41     
+ Misses       41156    41149    -7     

Impacted Files	Coverage Δ
src/analyses/constant_propagator.h	82.35% <ø> (ø)
src/ansi-c/expr2c.cpp	67.66% <ø> (+0.42%)	⬆️
src/goto-instrument/havoc_loops.cpp	0.00% <0.00%> (ø)
src/util/pointer_predicates.cpp	95.12% <ø> (+2.39%)	⬆️
src/util/pointer_predicates.h	100.00% <ø> (ø)
src/util/simplify_expr_class.h	90.47% <ø> (ø)
src/util/simplify_expr_pointer.cpp	86.58% <ø> (+0.75%)	⬆️
src/analyses/constant_propagator.cpp	95.46% <88.88%> (ø)
src/util/expr_util.cpp	90.55% <95.83%> (+0.81%)	⬆️
src/ansi-c/c_typecheck_expr.cpp	75.60% <100.00%> (ø)
... and 24 more

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