Add a Zenodo DOI for the 0.1.0 release

Include it in the changelog and a badge in the README (to be replaced
with the DOI for all versions once that's available).

README.rst

@@ -17,6 +17,9 @@ Part of the `Fatiando a Terra <https://www.fatiando.org>`__ project
 .. image:: https://img.shields.io/pypi/pyversions/ensaio.svg?style=flat-square
     :alt: Compatible Python versions.
     :target: https://pypi.python.org/pypi/ensaio
+.. image:: https://img.shields.io/badge/doi-10.5281%2Fzenodo.5784203-blue?style=flat-square
+    :alt: DOI used to cite Ensaio
+    :target: https://doi.org/10.5281/zenodo.5784203
 
 About
 -----

doc/changes.rst

@@ -6,11 +6,11 @@ Changelog
 Version 0.1.0
 -------------
 
-*Released on: 2021/12/23*
+Released on: 2021/12/23
 
-**First trial release of Ensaio** (Portuguese for "rehearsal"), a Python
-package for downloading open-access sample datasets for Geoscience.
-Used for testing our systems and implementation.
+doi:`10.5281/zenodo.5784203 <https://doi.org/10.5281/zenodo.5784203>`__
+
+First trial release of Ensaio. Used for testing our systems and implementation.
 
 This release contains contributions from:
 
@@ -24,9 +24,9 @@ This release contains contributions from:
 
     doi:`10.5281/zenodo.5784203 <https://doi.org/10.5281/zenodo.5784203>`__
 
-    **First release of Ensaio** (Portuguese for "rehearsal"), a Python package
-    for downloading open-access sample datasets for Geoscience. It taps into the
-    curated data collection in
+    **First major release of Ensaio** (Portuguese for "rehearsal"), a Python
+    package for downloading open-access sample datasets for Geoscience. It taps
+    into the curated data collection in
     `github.com/fatiando/data <https://github.com/fatiando/data>`__ and uses
     `Pooch <https://www.fatiando.org/pooch>`__ to manage downloading and caching
     the data files.