Add SpiderMonkey's GC Rooting Guide.

Author: ltratt

softdev.bib

@@ -3014,3 +3014,12 @@ @misc{speedometer
     year = {2022},
     author = {WebKit},
 }
+
+@misc{spidermonkey18rooting,
+    title = "{GC} Rooting Guide",
+    author = "Mozilla",
+    howpublished = {\url{https://github.com/mozilla-spidermonkey/spidermonkey-embedding-examples/blob/esr78/docs/GC\%20Rooting\%20Guide.md}},
+    year = "2018",
+    month = Sep,
+    note = "Accessed: 2023-03-03"
+}