Add changelog for v0.3.3 (#272)

Add changelog for version v0.3.3 and link to docs in README.rst.

Author: santisoler

README.rst

@@ -141,6 +141,7 @@ Documentation for other versions
 * `Development <http://www.fatiando.org/harmonica/dev>`__ (reflects the *master* branch on
   Github)
 * `Latest release <http://www.fatiando.org/harmonica/latest>`__
+* `v0.3.3 <http://www.fatiando.org/harmonica/v0.3.3>`__
 * `v0.3.2 <http://www.fatiando.org/harmonica/v0.3.2>`__
 * `v0.3.1 <http://www.fatiando.org/harmonica/v0.3.1>`__
 * `v0.3.0 <http://www.fatiando.org/harmonica/v0.3.0>`__

doc/changes.rst

@@ -3,6 +3,24 @@
 Changelog
 =========
 
+Version 0.3.3
+-------------
+
+*Released on: 2021/10/22*
+
+.. image:: https://zenodo.org/badge/DOI/10.5281/zenodo.5593112.svg
+   :alt: Digital Object Identifier for the Zenodo archive
+   :target: https://doi.org/10.5281/zenodo.5593112
+
+Bug fix:
+
+- Add ``EquivalentSources`` and ``EquivalentSourcesSph`` to API index. Replace the old equivalent layer classes. (`#270 <https://github.com/fatiando/harmonica/pull/270>`__)
+
+This release contains contributions from:
+
+- Santiago Soler
+
+
 Version 0.3.2
 -------------