docs: add the M-F and M-N keystrokes to the cheatsheet

doc/cheatsheet.html

@@ -66,6 +66,7 @@
 <tr><td>Ctrl+J</td><td>Justify paragraph or region</td></tr>
 <tr><td>Alt+J</td><td>Justify entire buffer</td></tr>
 <tr><td>Alt+B</td><td>Run a syntax check</td></tr>
+<tr><td>Alt+F</td><td>Run a "fixer"/formatter/arranger</td></tr>
 <tr><td>Alt+:</td><td>Start/stop recording of macro</td></tr>
 <tr><td>Alt+;</td><td>Replay macro</td></tr>
 </tbody></table>
@@ -116,6 +117,7 @@
 <tr><td>Alt+A</td><td>Turn the mark on/off</td></tr>
 <tr><td>Tab</td><td>Indent marked region</td></tr>
 <tr><td>Shift+Tab &nbsp;&nbsp;</td><td>Unindent marked region</td></tr>
+<tr><td>Alt+N</td><td>Turn line numbers on/off</td></tr>
 <tr><td>Alt+P</td><td>Turn visible whitespace on/off</td></tr>
 <tr><td>Alt+V</td><td>Enter next keystroke verbatim</td></tr>
 <tr><td>Ctrl+L</td><td>Refresh the screen</td></tr>