Add SlimerJS instructions

Author: quantum5

docs/site/pdf_generation.md

@@ -4,7 +4,10 @@ are distributed paper versions of the problems.
 
 For example, [here](https://dmoj.ca/problem/ioi14p1/pdf) is a generated PDF of [this problem](https://dmoj.ca/problem/ioi14p1).
 
-## Installing PhantomJS
+You can either use PhantomJS or SlimerJS to render PDFs.
+
+## PhantomJS
+
 Grab a PhantomJS build from [the download page](http://phantomjs.org/download.html), and extract it. For these static
 builds, there is no need to do anything further. You can run it to verify it's working.
 
@@ -13,7 +16,7 @@ $ phantomjs --version
 2.1.1
 ```
 
-## Configuring DMOJ to use PhantomJS
+### Configuring DMOJ to use PhantomJS
 Configuring DMOJ to generate PDFs with PhantomJS requires the addition of a couple of lines to your `local_settings.py`.
 
 ```py
@@ -26,6 +29,22 @@ PHANTOMJS = '/usr/local/bin/phantomjs'
 
 Restart DMOJ for the changes to take effect.
 
+## SlimerJS
+
+Grab a SlimerJS build from [here](https://github.com/DMOJ/site/files/2613909/slimerjs-1.0.0-firefox60.zip) and install Firefox 60 ESR.
+
+### Configuration
+
+```py
+# Cache location for generated PDFs. You should consider using something more persistant
+# than /tmp, since PDF generation is an expensive operation.
+PROBLEM_PDF_CACHE = '/tmp'
+# Path to wherever you extracted the SlimerJS binary.
+SLIMERJS = '/usr/local/bin/slimerjs'
+# Path to Firefox, if you installed it at a non-standard location:
+SLIMERJS_FIREFOX_PATH = '/usr/bin/firefox'
+```
+
 !!! note
     The DMOJ uses a Segoe UI font when viewed on Windows browsers. If running PhantomJS on a Linux server, installing
     Segoe UI fonts on it will provide optimal rendering quality — otherwise, a fallback font will be used and