adds sponsor link (#325)

Author: solegalli

README.md

@@ -213,3 +213,8 @@ Now you can build the docs using: ``sphinx-build -b html docs build``
 ## License
 
 BSD 3-Clause
+
+## Donate
+
+[Sponsor the maintainer](https://github.com/sponsors/solegalli) to support her continue expanding 
+Feature-engine.

docs/contribute/contribute_other.rst

@@ -34,4 +34,11 @@ straightaway.
 We are also happy to talk about the project in talks and podcasts. If you host a meetup
 or a podcast channel, do get in touch.
 
+Donate
+------
+
+If Feature-engine is helping your organization save money, time, effort, and frustrations,
+and be more productive, consider `sponsoring the maintainer <https://github.com/sponsors/solegalli>`_.
+This is a great way to show your appreciation. Thank you!
+
 For all of this, get in touch with the maintainer via `LinkedIn <https://www.linkedin.com/in/soledad-galli/>`_.

docs/contribute/index.rst

@@ -31,6 +31,7 @@ There are many ways to contribute to Feature-engine:
 - Improve our documentation, i.e., fix typos, improve grammar, or add more code examples.
 - Write a blog, tweet, or share our project with others.
 - Use Feature-engine in your lectures if you teach
+- `Sponsor the maintainer <https://github.com/sponsors/solegalli>`_.
 
 With plenty of ways to get involved, we would be happy for you to support the project.
 You only need to abide by the principles of openness, respect, and consideration of

docs/index.rst

@@ -213,6 +213,11 @@ let us know!
 For more details on how to contribute check the contributing page. Click on the
 :ref:`**Contribute** <contribute>` guide.
 
+Donate
+~~~~~~
+
+`Sponsor the maintainer <https://github.com/sponsors/solegalli>`_ to support her continue expanding
+Feature-engine.
 
 Open Source
 ~~~~~~~~~~~