docs: Fix ineffective escaping, emphasize error messages

[bittner]

As discussed in #1668 (comment):

Fixes the broken markup by using HTML entities.

In addition, I used slanted font (emphasized) for the error messages to make it clearer how to interpret the text.

[sisp]

Prettier is unhappy again:

       > index ce26b42..ec9dec4 100644
       > --- a/docs/updating.md
       > +++ b/docs/updating.md
       > @@ -216,9 +216,9 @@ the introduced changes to your code base, specifically when you have unpleasant
       >  conflicts, it's not 100% obvious how to get back to the previously clean copy of your
       >  branch. The following strategies won't work:
       >  
       > --   `git checkout <branch>` – *error: you need to resolve your current index first*
       > --   `git checkout .` – *error: path '&lt;filename&gt;' is unmerged*
       > --   `git merge --abort` – *fatal: There is no merge to abort (MERGE_HEAD missing)*
       > +-   `git checkout <branch>` – _error: you need to resolve your current index first_
       > +-   `git checkout .` – _error: path '&lt;filename&gt;' is unmerged_
       > +-   `git merge --abort` – _fatal: There is no merge to abort (MERGE_HEAD missing)_
       >  
       >  Here is what you can do using Git in the terminal to throw away all changes:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.38%. Comparing base (b581d8d) to head (8901287).
Report is 70 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1671      +/-   ##
==========================================
+ Coverage   97.32%   97.38%   +0.05%     
==========================================
  Files          49       49              
  Lines        5004     5004              
==========================================
+ Hits         4870     4873       +3     
+ Misses        134      131       -3     

Flag	Coverage Δ
unittests	97.38% <ø> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[sisp]

LGTM, thanks!