Inaccurate version support description in README

[alanag13]

The README states that node v20 and up are supported, but attempting to run with node v20.2.0 produces:

file:///Users/redacted/.npm/_npx/191c568aa03d4fb8/node_modules/mongodb-mcp-server/dist/helpers/packageInfo.js:1
import packageJson from "../../package.json" with { type: "json" };
                                             ^^^^

SyntaxError: Unexpected token 'with'
    at DefaultModuleLoader.moduleStrategy (node:internal/modules/esm/translators:116:18)
    at DefaultModuleLoader.moduleProvider (node:internal/modules/esm/loader:206:14)

All works as expected on newer versions of node.