docs: update installation instructions in README (#22)

Author: IanSkelskey

README.md

@@ -30,7 +30,7 @@ Automates the creation of standardized Git commit messages using [OpenAI's API](
 
 ## Installation Instructions
 
-Commit Generator can be installed using npm:
+Commit Generator can be installed globally using npm:
 
 ```bash
 npm install -g ai-diff-commit

package.json

@@ -2,6 +2,7 @@
     "name": "ai-diff-commit",
     "version": "0.0.2",
     "description": "A CLI tool to generate commit messages using AI, powered by OpenAI.",
+    "preferGlobal": true,
     "main": "dist/main.js",
     "bin": {
         "ai-diff-commit": "dist/main.js"