added pyright badge
[![Linted with flake8](https://img.shields.io/badge/lint-flake8-%231674b1)](https://flake8.pycqa.org)
[![Linted with pylint](https://img.shields.io/badge/lint-pylint-%231674b1)](https://pylint.pycqa.org)
[![Checked with mypy](https://img.shields.io/badge/type--check-mypy-%231674b1)](http://mypy-lang.org/)
+[![Checked with pyright](https://img.shields.io/badge/type--check-pyright-%231674b1)](https://github.com/microsoft/pyright)
[![security: bandit](https://img.shields.io/badge/security-bandit-yellow.svg)](https://github.com/PyCQA/bandit)
[![PyPI version](https://img.shields.io/pypi/v/btclib.svg)](https://pypi.python.org/pypi/btclib/)
[![Build Status](https://travis-ci.org/btclib-org/btclib.svg)](https://travis-ci.org/btclib-org/btclib)
