Document where build.commands working directory

Author: LecrisUT

docs/user/config-file/v2.rst

@@ -487,6 +487,10 @@ The ``$READTHEDOCS_OUTPUT/html`` directory will be uploaded and hosted by Read t
 
    ``build.os`` and ``build.tools`` are also required when using ``build.commands``.
 
+.. note::
+
+   All items in the ``build.commands`` array are executed from the same initial working directory, i.e. the git repository root.
+
 :Type: ``list``
 :Required: ``false``
 :Default: ``[]``