update README

README.md

@@ -2,6 +2,8 @@
 
 [![CC BY-NC-SA 4.0][cc-by-nc-sa-shield]][cc-by-nc-sa]
 
+***You can find the PDF file on the Releases page on the right ===>>>***
+
 ## About
 
 > ***It soon became clear that the unconscious instincts for logic and language which had enabled me to succeed were not shared by the large majority of my students.*** - Susanna Epp (author of [Discrete Mathematics with Applications, 5th edition](https://www.amazon.com/Discrete-Mathematics-Applications-Susanna-Epp-ebook/dp/B07M87BWRC))
@@ -18,10 +20,18 @@ Please feel free to [open a discussion](https://github.com/spamegg1/Epp-Discrete
 
 Contact me: `spamegg1` on Discord, or [on Slack](https://join.slack.com/t/spamegg/shared_invite/zt-1vhzofzrl-ucBjeQEQkl9Ol3wpvL9VPw), or [on Matrix](https://matrix.to/#/!GQFJgtvxFByBVixTAi:matrix.org?via=matrix.org)
 
+## Contributing
+
+Only edit the `.tex` source files, I will use Github actions to compile and release the PDF files. (work in progress)
+
+To make a change to an exercise, you need to change 2 files:
+
+- one of the chapter files, say `chapter5.tex` for example, and
+- make the same change in `all.tex` in the relevant section.
+
 ## TODO
 
 - Add [Github actions](https://github.com/marketplace/actions/github-action-for-latex)
 
 [cc-by-nc-sa]: http://creativecommons.org/licenses/by-nc-sa/4.0/
-[cc-by-nc-sa-image]: https://licensebuttons.net/l/by-nc-sa/4.0/88x31.png
 [cc-by-nc-sa-shield]: https://img.shields.io/badge/License-CC%20BY--NC--SA%204.0-lightgrey.svg