Fix typo.

Closes #709

Author: jlevy

README.md

@@ -4,7 +4,7 @@
 
 # The Art of Command Line
 
-*Note: I'm planning to revise this and looking for a new co-author to help with expanding this into a more comprehensive guide. While it's very popoular, it could be broader and a bit deeper. If you like to write and are close to being an expert on this material and willing to consider helping, please drop me a note at josh (0x40) holloway.com. –[jlevy](https://github.com/jlevy), [Holloway](https://www.holloway.com). Thank you!*
+*Note: I'm planning to revise this and looking for a new co-author to help with expanding this into a more comprehensive guide. While it's very popular, it could be broader and a bit deeper. If you like to write and are close to being an expert on this material and willing to consider helping, please drop me a note at josh (0x40) holloway.com. –[jlevy](https://github.com/jlevy), [Holloway](https://www.holloway.com). Thank you!*
 
 - [Meta](#meta)
 - [Basics](#basics)