DOCS-15579 capped collections update (#1739)

* DOCS-15579-capped-collections-update

* DOCS-15579-capped-collections-update

* DOCS-15579-capped-collections-update

* DOCS-15579-capped-collections-update

Co-authored-by: jason-price-mongodb <[email protected]>

Author: jason-price-mongodb

source/core/capped-collections.txt

@@ -228,6 +228,12 @@ You can resize a capped collection using the :dbcommand:`collMod` command's
 ``cappedSize`` option to set the ``cappedSize`` in bytes. ``cappedSize`` must be 
 greater than ``0`` and less than ``1e+15`` (1 PB). 
 
+.. note::
+
+   Before you can resize a capped collection, you must have already set
+   the :ref:`featureCompatibilityVersion <set-fcv>` to at least version
+   ``"6.0"``.
+
 For example, the following command sets the maximum size of the ``"log"`` capped 
 collection to 100000 bytes: