Fix case of README file in setup.py

Author: ef1500

setup.py

@@ -22,7 +22,7 @@
     author="EF1500",
     author_email="rosemilovelockofficial@proton.me",
     description="Bound Book Format (BBF) tools and bindings",
-    long_description=open("README.md").read(),
+    long_description=open("readme.md").read(),
     long_description_content_type="text/markdown",
     url="https://github.com/ef1500/libbbf",
 
@@ -43,4 +43,4 @@
 
     zip_safe=False,
     python_requires=">=3.7",
-)
+)