Docs: abort_on_unused_inputs (ECP-WarpX#3364)

* Document abort_on_unused_inputs

* Fix default

Co-authored-by: Axel Huebl <axel.huebl@plasma.ninja>

Docs/source/usage/parameters.rst

@@ -139,6 +139,10 @@ Overall simulation parameters
     Note that even with this set to ``1`` WarpX will not catch all out-of-memory events yet when operating close to maximum device memory.
     `Please also see the documentation in AMReX <https://amrex-codes.github.io/amrex/docs_html/GPU.html#inputs-parameters>`_.
 
+* ``amrex.abort_on_unused_inputs`` (``0`` or ``1``; default is ``0`` for false)
+    When set to ``1``, this option causes simulation to fail *after* its completion if there were unused parameters.
+    It is mainly intended for continuous integration and automated testing to check that all tests and inputs are adapted to API changes.
+
 Signal Handling
 ^^^^^^^^^^^^^^^