Document how to provide custom styling in soy template

Change-Id: Ifce13ba2eacfae136b1d7c41c1a45d09dcafcbaa
diff --git a/Documentation/ b/Documentation/
index 9f41e45..65727e5 100644
--- a/Documentation/
+++ b/Documentation/
@@ -59,6 +59,28 @@
 customTemplates = path/to/
+### Custom styling
+It's possible to inject custom styles within the template. To do this add
+the following to `gitiles.config`:
+    customTemplates = path/to/
+    customVariant=aVariant
+Where `customVariant` is the variable defined in the default
+templates themselves. Then you can define `` as follows:
+{namespace gitiles}
+{deltemplate gitiles.customHeadTagPart variant="'aVariant'"}
+<link rel="stylesheet" type="text/css" href="/static/file.css" />
+It is also possible to define a `<style>` tag there if desired.
 ### Fixed time zone
 By default dates are formatted including the local user time zone as that