Merge pull request #194 from jhlegarreta/doc/add-external-dep-details

DOC: Improve instructions for required external dependencies

Author: jhlegarreta

docs/installation.rst

@@ -17,4 +17,9 @@ Check your installation with the following command line ::
 
 External Dependencies
 ---------------------
-*nifreeze* requires DIPY_, and ANTs_.
+*nifreeze* requires ANTs_, which is leveraged through the Nipype_ Python
+interface for registration purposes. There are
+[several ways to install ``ANTs``](https://github.com/ANTsX/ANTs?tab=readme-ov-file#installation).
+Notably, the path to the installed binaries needs to be added to the ``PATH`` ::
+
+   $ export PATH=/path/to/ants/bin:$PATH