Fix Markdown syntax

[mernst]

This fixes incorrect Markdown syntax.
You can see the bad formatting just above https://github.com/diffblue/cbmc/blob/develop/COMPILING.md#compiling-with-make-on-linux .

• 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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.77%. Comparing base (f88ea70) to head (963929c).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #9109   +/-   ##
========================================
  Coverage    80.77%   80.77%           
========================================
  Files         1712     1712           
  Lines       189814   189814           
  Branches        73       73           
========================================
  Hits        153328   153328           
  Misses       36486    36486           

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