add Lint action & add badges

.github/workflows/black.yml

@@ -0,0 +1,10 @@
+name: Lint
+
+on: [push, pull_request]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: psf/black@stable

README.md

@@ -1,5 +1,7 @@
 # FSRS Optimizer
 
+[![PyPi](https://img.shields.io/pypi/v/FSRS-Optimizer)](https://pypi.org/project/FSRS-Optimizer/) [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
+
 The FSRS Optimizer is a Python library capable of utilizing personal spaced repetition review logs to refine the FSRS algorithm. Designed with the intent of delivering a standardized, universal optimizer to various FSRS implementations across numerous programming languages, this tool is set to establish a ubiquitous standard for spaced repetition review logs. By facilitating the uniformity of learning data among different spaced repetition softwares, it guarantees learners consistent review schedules across a multitude of platforms.
 
 Delve into the underlying principles of the FSRS Optimizer's training process at: https://github.com/open-spaced-repetition/fsrs4anki/wiki/The-mechanism-of-optimization