Update align.rst

Helpful to know what a base map is?

source/align.rst

@@ -8,6 +8,6 @@ Starting from ODM ``3.0.2`` people can supply a reference alignment file to geor
 
 If you supply a file called ``align.laz``, ``align.las`` or ``align.tif`` (single band GeoTIFF DEM) then ODM will automatically detect it and attempt to align outputs to this reference model. If it has another name you can specify using ``--align <path>``.
 
-The alignment file must be created in the base of your project folder.
+The alignment file must be created in the base of your project folder. The base folder is usually where you have stored your images.
 
 `Learn to edit <https://github.com/opendronemap/docs#how-to-make-your-first-contribution>`_ and help improve `this page <https://github.com/OpenDroneMap/docs/blob/publish/source/align.rst>`_!