Add beta changelog to the blog post (#2326)

Meet the new Tarantool beta release of August 2021: v. 2.10.0-beta1.

Proofread by Kseniia Antonova and Patience Daur, translated by ainoneko, translation reviewed by Patience Daur.

Co-authored-by: Patience Daur <patiencedaur@gmail.com>
Co-authored-by: ainoneko <ainoneko@gmail.com>

Author: 3 people