mendel: Add the manifest project to the... erm... manifest.

This is to make sure the manifest is checked out in our internal build systems
so that we can generate a reproducible build by reading and generating a
manifest with the correct sha-1 sums in place.

Change-Id: I5119942d59bb3515d9afc9fabb75615d150e5738
diff --git a/mendel.xml b/mendel.xml
index be8f9f1..5db7cbf 100644
--- a/mendel.xml
+++ b/mendel.xml
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <manifest>
-
     <remote fetch="https://coral.googlesource.com" name="coral"
       review="https://coral-review.googlesource.com" />
     <remote fetch="sso://aiyprojects" name="coral-internal"
@@ -8,6 +7,8 @@
 
     <default remote="coral" revision="master" />
 
+    <project name="manifest" path="manifest" />
+
     <project name="docs" path="docs">
       <linkfile src="GettingStarted.md" dest="GettingStarted.md" />
     </project>