Update of vosk with help of @nshmyrev

Last part - Updating readme

Author: mytja

README.rst

@@ -54,6 +54,8 @@ The `library reference <https://github.com/Uberi/speech_recognition/blob/master/
 
 See `Notes on using PocketSphinx <https://github.com/Uberi/speech_recognition/blob/master/reference/pocketsphinx.rst>`__ for information about installing languages, compiling PocketSphinx, and building language packs from online resources. This document is also included under ``reference/pocketsphinx.rst``.
 
+You have to install Vosk models for using Vosk. `Here <https://alphacephei.com/vosk/models>`__ are models avaiable. You have to place them in models folder of your project, like "your-project-folder/models/your-vosk-model"
+
 Examples
 --------
 
@@ -132,6 +134,16 @@ Note that the versions available in most package repositories are outdated and w
 
 See `Notes on using PocketSphinx <https://github.com/Uberi/speech_recognition/blob/master/reference/pocketsphinx.rst>`__ for information about installing languages, compiling PocketSphinx, and building language packs from online resources. This document is also included under ``reference/pocketsphinx.rst``.
 
+Vosk (for Vosk users)
+~~~~~~~~~~~~~~~~~~~~~
+Vosk API is **required if and only if you want to use Vosk recognizer** (``recognizer_instance.recognize_vosk``).
+
+You can install it with ``python3 -m pip install vosk``.
+
+You also have to install Vosk Models:
+
+`Here <https://alphacephei.com/vosk/models>`__ are models avaiable for download. You have to place them in models folder of your project, like "your-project-folder/models/your-vosk-model"
+
 Google Cloud Speech Library for Python (for Google Cloud Speech API users)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~