Move rapids_cpm_package_override to CPM section of docs (#462)

Authors:
  - Robert Maynard (https://github.com/robertmaynard)

Approvers:
  - Bradley Dice (https://github.com/bdice)

URL: #462

docs/api.rst

@@ -33,6 +33,7 @@ tracking of these dependencies for correct export support.
 
    /command/rapids_cpm_init
    /command/rapids_cpm_find
+   /command/rapids_cpm_package_override
 
 CPM Pre-Configured Packages
 ***************************
@@ -57,7 +58,6 @@ package uses :ref:`can be found here. <cpm_versions>`
    /packages/rapids_cpm_rmm
    /packages/rapids_cpm_spdlog
    /packages/rapids_cpm_thrust
-   /command/rapids_cpm_package_override
 
 .. _`cython`: