DOCS-353 killOp and foreground index ops

Author: Bob Grabar

source/reference/limits.txt

@@ -141,6 +141,12 @@ Operations
 
    .. see:: :operator:`$or` and :doc:`/core/geospatial-indexes`.
 
+.. _cannot-kill-foreground:
+.. limit:: Cannot Kill Foreground Index Build
+
+   You cannot use :method:`db.killOp()` to kill a foreground index
+   build.
+
 Naming Restrictions
 ~~~~~~~~~~~~~~~~~~~
 

source/reference/method/db.killOp.txt

@@ -13,4 +13,7 @@ db.killOp()
    :doc:`/reference/current-op` for full documentation of the output
    of :method:`db.currentOp()`.
 
+   .. note:: You cannot use :method:`db.killOp()` to kill a foreground
+      index build.
+
    .. include:: /includes/warning-terminating-operations.rst