doc: update examples of the final "callback" argument for fs.access()

doc/api/fs.md

@@ -760,12 +760,35 @@ no effect on Windows (will behave like `fs.constants.F_OK`).
 
 The final argument, `callback`, is a callback function that is invoked with
 a possible error argument. If any of the accessibility checks fail, the error
-argument will be an `Error` object. The following example checks if the file
-`/etc/passwd` can be read and written by the current process.
+argument will be an `Error` object. The following examples check if
+`package.json` exists, and if it is readable or writable.
 
 ```js
-fs.access('/etc/passwd', fs.constants.R_OK | fs.constants.W_OK, (err) => {
-  console.log(err ? 'no access!' : 'can read/write');
+const file = 'package.json';
+
+// Check if the file exists in the current directory.
+fs.access(file, fs.constants.F_OK, (err) => {
+  console.log(`${file} ${err ? 'does not exist' : 'exists'}`);
+});
+
+// Check if the file is readable.
+fs.access(file, fs.constants.R_OK, (err) => {
+  console.log(`${file} ${err ? 'is not readable' : 'is readable'}`);
+});
+
+// Check if the file is writable.
+fs.access(file, fs.constants.W_OK, (err) => {
+  console.log(`${file} ${err ? 'is not writable' : 'is writable'}`);
+});
+
+// Check if the file exists in the current directory, and if it is writable.
+fs.access(file, fs.constants.F_OK | fs.constants.W_OK, (err) => {
+  if (err) {
+    console.error(
+      `${file} ${err.code === 'ENOENT' ? 'does not exist' : 'is read-only'}`);
+  } else {
+    console.log(`${file} exists, and it is writable`);
+  }
 });
 ```