added acknowledgements

Author: learnbyexample

README.md

@@ -40,6 +40,25 @@ For a preview of the book, see [sample chapters](https://github.com/learnbyexamp
 
 <br>
 
+# Acknowledgements
+
+* [GNU grep documentation](https://www.gnu.org/software/grep/manual/grep.html) - manual and examples
+* [ripgrep](https://github.com/BurntSushi/ripgrep) - user guide and examples
+* [stackoverflow](https://stackoverflow.com/) and [unix.stackexchange](https://unix.stackexchange.com/) - for getting answers to pertinent questions on `bash`, `grep` and other commands
+* [tex.stackexchange](https://tex.stackexchange.com/) - for help on `pandoc` and `tex` related questions
+* Cover image
+    * [draw.io](https://about.draw.io/)
+    * [finding a needle in a haystack](https://commons.wikimedia.org/wiki/File:Wikipe-tan_on_the_haystack.png) by [Mikael Häggström](https://commons.wikimedia.org/wiki/User:Mikael_H%C3%A4ggstr%C3%B6m) under [Creative Commons Attribution-Share Alike 3.0 Unported](https://creativecommons.org/licenses/by-sa/3.0/deed.en) (modified to remove Wikimedia logo)
+    * [train icon](https://www.iconfinder.com/icons/4213874/metro_train_transport_transportation_travelling_vehicle_icon) by [Yasir Masood](https://www.iconfinder.com/Muhammad_Auns) under [Creative Commons Attribution 3.0 Unported](https://creativecommons.org/licenses/by/3.0/)
+    * [plane icon](https://www.iconfinder.com/icons/3671993/airplane_filled_fly_plane_sky_travel_icon) by [Pondok Multimedia](https://www.iconfinder.com/Ontimedia)
+* [softwareengineering.stackexchange](https://softwareengineering.stackexchange.com/questions/39/whats-your-favourite-quote-about-programming) and [skolakoda](https://skolakoda.org/programming-quotes) for programming quotes
+* [Warning](https://commons.wikimedia.org/wiki/File:Warning_icon.svg) and [Info](https://commons.wikimedia.org/wiki/File:Info_icon_002.svg) icons by [Amada44](https://commons.wikimedia.org/wiki/User:Amada44) under public domain
+* [Andrew Gallant](https://blog.burntsushi.net/about/) (author of `ripgrep`) for critical feedback
+
+Special thanks to all my friends and online acquaintances for their help, support and encouragement, especially during difficult times.
+
+<br>
+
 # License
 
 The code snippets are licensed under MIT, see [LICENSE](./LICENSE) file