Fix typo in readme

Co-authored-by: Maarten Sebregts <110895564+maarten-ic@users.noreply.github.com>

Author: olivhoenen

README.md

@@ -21,7 +21,7 @@ More details are described in the documentation generated from `/docs/source/ins
 The documentation is autogenerated from the source using [Sphinx](http://sphinx-doc.org/)
 and can be found at the [readthedocs](https://imas-python.readthedocs.io/en/latest/)
 
-To generated the documentation yourself, install the ``docs`` optional dependencies and do:
+To generate the documentation yourself, install the ``docs`` optional dependencies and do:
 ```bash
 make -C docs html
 ```