[doc] Split Earlgrey spec into Datasheet and Specification

Signed-off-by: Michael Schaffner <msf@google.com>
diff --git a/_index.md b/_index.md
index 5d7fb10..80ffd30 100644
--- a/_index.md
+++ b/_index.md
@@ -26,3 +26,7 @@
 ## Documentation Sections
 
 {{% sectionContent type="section" depth="1" %}}
+
+## Datasheets
+
+* [OpenTitan Earl Grey Chip Datasheet]({{< relref "hw/top_earlgrey/doc" >}})