doc/rcu: fix typo

Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Message-Id: <1472696479-3619-1-git-send-email-caoj.fnst@cn.fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/docs/rcu.txt b/docs/rcu.txt
index 2f70954..a70b72c 100644
--- a/docs/rcu.txt
+++ b/docs/rcu.txt
@@ -37,7 +37,7 @@
 there cannot be any readers who hold references to the data structure,
 and these can now be safely reclaimed (e.g., freed or unref'ed).
 
-Here is a picutre:
+Here is a picture:
 
         thread 1                  thread 2                  thread 3
     -------------------    ------------------------    -------------------