Added sphinx-rtd-theme==0.5.2 as a dependency to Sphinx requirements.txt since it is not a hard dependency anymore.

Author: lmarini

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## UNRELEASED
+
+### Changed
+- Added sphinx-rtd-theme==0.5.2 as a dependency to Sphinx requirements.txt since it is not a hard dependency anymore.
+
 ## 1.16.0 - 2021-03-31
 
 ### Fixed

doc/src/sphinx/requirements.txt

@@ -25,3 +25,4 @@ sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-qthelp==1.0.3
 sphinxcontrib-serializinghtml==1.1.4
 urllib3==1.25.9
+sphinx-rtd-theme==0.5.2