Add a 'theme' for OMP, so the internal themes don't clash with it. (#2100)

* Add a 'theme' for OMP, so the internal themes don't clash with it.

* Add theme to clean_files

* Add screenshot to the docs

* Correct the name of the default theme in the docs.

* keeping it cleaner

Co-authored-by: Ira Abramov <github@ira.abramov.org>

docs/themes-list/index.rst

@@ -346,6 +346,19 @@ NWinkler
    :alt:
 
 
+----
+
+.. _oh_my_posh_image:
+
+Oh-My-Posh
+^^^^^^^^^^
+
+
+.. image:: https://bash-it.github.io/bash-it/docs/images/oh-my-posh.png
+   :target: https://bash-it.github.io/bash-it/docs/images/oh-my-posh.png
+   :alt:
+
+
 ----
 
 Pete