fix: Use README.md for package description

Author: 薛華慶, james.hsueh

MANIFEST.in

@@ -1,6 +1,6 @@
 # Include essential files
 include LICENSE
-include INSTALLER_README.md
+include README.md
 include pyproject.toml
 include gsi_installer.py
 

pyproject.toml

@@ -8,7 +8,7 @@ authors = [
 maintainers = [
     {name = "GSI-Protocol Contributors"}
 ]
-readme = "INSTALLER_README.md"
+readme = "README.md"
 requires-python = ">=3.10"
 license = {text = "MIT"}
 keywords = ["gsi-protocol", "sdd", "bdd", "gherkin", "claude", "codex", "ai", "workflow", "spec-driven-development"]
@@ -49,7 +49,7 @@ only-include = ["gsi_installer.py"]
 only-include = [
     "gsi_installer.py",
     "pyproject.toml",
-    "INSTALLER_README.md",
+    "README.md",
     "LICENSE",
     "MANIFEST.in"
 ]