Add spell checking to vim cheatsheet (#497)

* Add spell checking to vim cheatsheet

* Add backticks for command formatting

vim.md

@@ -363,6 +363,20 @@ Do this in insert mode.
 
 Works like `:qa`, but throws an error. Great for aborting Git commands.
 
+### Spell checking
+
+| Shortcut                     | Description                                           |
+| ---                          | ---                                                   |
+| `:set spell spelllang=en_us` | Turn on US English spell checking                     |
+| `]s`                         | Move to next misspelled word after the cursor         |
+| `[s`                         | Move to previous misspelled word before the cursor    |
+| `z=`                         | Suggest spellings for the word under/after the cursor |
+| `zg`                         | Add word to spell list                                |
+{: .-shortcuts}
+
+See `:help spell`
+
+
 Also see
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