slide example: Add link to slide printing instructions

The printing instructions seem to not be really clear. Linking the
reveal.js offical docs should help.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

Author: SISheogorath

public/docs/slide-example.md

@@ -270,7 +270,7 @@ Press `B` or `.` on your keyboard to pause the presentation. This is helpful whe
 
 Down below you can find a print icon<i class="fa fa-fw fa-print"></i>.
 
-After you click on it, use the print function of your browser (either CTRL+P or cmd+P) to print the slides as PDF.
+After you click on it, use the print function of your browser (either CTRL+P or cmd+P) to print the slides as PDF. [See official reveal.js instructions for details](https://github.com/hakimel/reveal.js#instructions-1)
 
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