Use bolded HTML entities for the four arrows, instead of the literal
triangular Unicode "arrows" which many fonts don't include.
This addresses https://savannah.gnu.org/bugs/?57505.
The word "fixer" sounds too much as if the command would be able
to fix mistakes or correct errors. Especially when seen next to
"linter", it sounds as if one does a syntax check and the other
fixes the found mistakes. (Although the command might in theory
be used for this, it is not its intended purpose.)
It's in a two-column format that fits on a single page, and uses the
more widely known Ctrl+X and Alt+X notations (instead of ^X and M-X).
The file is published on https://nano-editor.org/cheatsheet.html.
