Set up admonitions for GitHub environment

Author: savvan0h

README.adoc

@@ -18,6 +18,13 @@
 :sectnums:
 :imagesdir: images
 :icons: font
+ifdef::env-github[]
+:tip-caption: :bulb:
+:note-caption: :information_source:
+:important-caption: :heavy_exclamation_mark:
+:caution-caption: :fire:
+:warning-caption: :warning:
+endif::[]
 
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