Update ReceivePackInitializer plugin docs

It's sad but true that implementers need to understand this portion of
Gerrit/JGit internals to implement a plugin correctly.

Change-Id: I57bf16c326962512401e273ad1e2e9de689b0639

Documentation/dev-plugins.txt

diff --git a/Documentation/dev-plugins.txt b/Documentation/dev-plugins.txt
index ad2c50c..9117d65 100644
--- a/Documentation/dev-plugins.txt
+++ b/Documentation/dev-plugins.txt
@@ -482,10 +482,15 @@
 [[receive-pack]]
 == Receive Pack Initializers
 
-Plugins may provide ReceivePack initializers which will be invoked
-by Gerrit just before a ReceivePack instance will be used. Usually,
-plugins will make use of the setXXX methods on the ReceivePack to
-set additional properties on it.
+Plugins may provide ReceivePackInitializer instances, which will be
+invoked by Gerrit just before a ReceivePack instance will be used.
+Usually, plugins will make use of the setXXX methods on the ReceivePack
+to set additional properties on it.
+
+The interactions with the core Gerrit ReceivePack initialization and
+between ReceivePackInitializers can be complex. Please read the
+ReceivePack Javadoc and Gerrit AsyncReceiveCommits implementation
+carefully.
 
 [[post-receive-hook]]
 == Post Receive-Pack Hooks