Ways to improve the documentation

Vosk is really incredible and I think a few improvements to the documentation would help increase the number of people that are able to use it.

* **Website**: The documentation is mostly external [here](https://alphacephei.com/vosk/). I am unaware of a way to submit it patch to the website. The website is overall good, but not exhaustive. It would be nice to allow the community to help.
* **Documentation for example directories**: The website has instructions for how to use some of the examples in specific ways. There are many more example scripts than are listed on the website. It would be helpful to have documentation for the list of the example scripts along with a brief description of what they set out to do. For example, creating the file `vosk-api/python/example/README.md` would be a logical place for such a list for the python scripts. I initially thought that `test_speaker.py` would translate the output device like an opposite for `test_microphone.py` and it was not until I read the entirety of the file and looked up a description of vosk-model-spk-0.4 that I understood that it was for differentiating between who was speaking.
* **Example documentation**: The example scripts are very helpful, but there is very little documentation within the scripts. To understand what they do, the user often has to read external documentation on how to use the script, understand the title, try them blindly, or skim over the entirety of the script. A comment at the beginning of the script with the intended purpose would be helpful. Descriptions of function purposes would be helpful for those that are novice programmers.

I thought about submitting a pull request for some of these changes, but I do not have a strong grasp of what all of the examples do yet so maybe someone more familiar with them would do a better job.