Bump version number to 2.2.1.

PiperOrigin-RevId: 461471944
Change-Id: Ia752d992fabdc57b822bc30b01030c19162917ac

doc/changelog.rst

@@ -2,14 +2,18 @@
 Changelog
 =========
 
-Upcoming version (not yet released)
------------------------------------
+.. Upcoming version (not yet released)
+.. -----------------------------------
+
+Version 2.2.1 (July 18, 2022)
+-----------------------------
 
 General
 ^^^^^^^
 
 - Added ``mjd_transitionFD`` to compute efficient finite difference approximations of the state-transition and
   control-transition matrices, :ref:`see here<derivatives>` for more details.
+- Added derivatives for the ellipsoid fluid model.
 - Added ``ctrl`` attribute to :ref:`keyframes<keyframe>`.
 - Added ``clock`` sensor which :ref:`measures time<sensor-clock>`.
 - Added visualisation groups to skins.
@@ -23,7 +27,7 @@ General
 - Add memory poisoning when building with Address Sanitizer (ASAN) and Memory Sanitizer (MSAN). This allows ASAN to
   detect reads and writes to regions in ``mjModel.buffer`` and ``mjData.buffer`` that do not lie within an array, and
   for MSAN to detect reads from uninitialised fields in ``mjData`` following ``mj_resetData``.
-
+- Add a `slider-crank example <https://github.com/deepmind/mujoco/tree/2.2.1/model/slider_crank>`_ to ``model/``.
 
 Bug fixes
 ^^^^^^^^^

doc/unity.rst

@@ -29,14 +29,14 @@ _____
 
 The MuJoCo app needs to be run at least once before the native library can be used, in order to register the library as
 a trusted binary. Then, copy the dynamic library file from
-``/Applications/MuJoCo.app/Contents/Frameworks/mujoco.framework/Versions/Current/libmujoco.2.2.0.dylib`` (it can be
+``/Applications/MuJoCo.app/Contents/Frameworks/mujoco.framework/Versions/Current/libmujoco.2.2.1.dylib`` (it can be
 found by browsing the contents of ``MuJoCo.app``) and rename it as ``mujoco.dylib``.
 
 Linux
 _____
 
 Expand the ``tar.gz`` archive to ``~/.mujoco``. Then copy the dynamic library from
-``~/.mujoco/mujoco-2.2.0/lib/libmujoco.so.2.2.0`` and rename it as ``libmujoco.so``.
+``~/.mujoco/mujoco-2.2.1/lib/libmujoco.so.2.2.1`` and rename it as ``libmujoco.so``.
 
 Windows
 _______