docs: credits for asciinema (#190)

README.md

@@ -19,6 +19,7 @@ If you find this book useful, please do consider [sponsoring me](https://github.
 * [Versioning](#versioning)
 * [Contributing](#contributing)
 * [Copyright & Licensing](#copyright--licensing)
+* [ASCII Terminal Recordings](#ascii-terminal-recordings)
 * [Thanks!](#thanks)
 * [Contributors ✨](#contributors-)
 
@@ -105,6 +106,10 @@ All content is Copyright (©) Dave Kerr. Please get in touch by opening an issue
 
 This work is licensed under a [Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License](http://creativecommons.org/licenses/by-nc-sa/3.0/).
 
+## ASCII Terminal Recordings
+
+All terminal recordings used in this project are built using the superb '[asciinema](https://asciinema.org/)' tool. Many thanks to Marcin Kulik for building such an excellent piece of software.
+
 ## Thanks!
 
 Thanks to the following people who have helped with reviews, comments, suggestions.