docs: add 0.22 migration article

docs/en/SUMMARY.md

@@ -84,6 +84,7 @@
   * [LED strip (legacy)](leds_old.md)
   * [Contribution Guidelines](contributing.md)
   * [Migration to v0.20](migrate20.md)
+  * [Migration to v0.22](migrate22.md)
 * [Clover-based projects](projects.md)
   * [Drone show](clever-show.md)
   * [Innopolis Open 2020 (L22_ÆRO)](innopolis_open_L22_AERO.md)

docs/en/migrate22.md

@@ -0,0 +1,49 @@
+# Migration to version 0.20
+
+## Python 3 transition
+
+Python 2 is deprecated since January 1st, 2020. The Clover platform moves to Python 3.
+
+For running flight script instead of `python` command:
+
+```bash
+python flight.py
+```
+
+use `python3` command:
+
+```bash
+python3 flight.py
+```
+
+Python 3 has certain syntax differences in comparison with the old version. Instead of `print` *operator*:
+
+```python
+print 'Clover is the best'
+```
+
+use `print` *function*:
+
+```python
+print('Clover is the best')
+```
+
+The division operator operates floating points by default (instead of integer). Python 2:
+
+```python
+>>> 10 / 4
+2
+```
+
+Python 3:
+
+```python
+>>> 10 / 4
+2.5
+```
+
+For strings `unicode` type is used by default (instead of `str` type).
+
+Encoding specification (`# coding: utf8`) is not necessary any more.
+
+More details on all the language changes see in [appropriate article](https://sebastianraschka.com/Articles/2014_python_2_3_key_diff.html).