docs: added jsdocs to update-version generated output

src.ts/_admin/update-version.ts

@@ -19,9 +19,8 @@ async function getNpmPackage(name: string): Promise<any> {
 
     return cache[name] || null;
 }
-
 function writeVersion(version: string): void {
-    const content = `export const version: string = "${ version }";\n`;
+    const content = `/* Do NOT modify this file; see /src.ts/_admin/update-version.ts */\n\n/**\n *  The current version of Ethers.\n */\nexport const version: string = "${ version }";\n`;
     atomicWrite(resolve("src.ts/_version.ts"), content);
 }