doc: add descriptions about when options.mode is ignored

doc/api/fs.md

@@ -659,6 +659,9 @@ exist. `data` can be a string or a {Buffer}.
 
 If `options` is a string, then it specifies the `encoding`.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 The `path` may be specified as a {FileHandle} that has been opened
 for appending (using `fsPromises.open()`).
 
@@ -1374,6 +1377,9 @@ The `encoding` option is ignored if `data` is a buffer.
 
 If `options` is a string, then it specifies the encoding.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 Any specified {FileHandle} has to support writing.
 
 It is unsafe to use `fsPromises.writeFile()` multiple times on the same file
@@ -1640,6 +1646,9 @@ changes:
 Asynchronously append data to a file, creating the file if it does not yet
 exist. `data` can be a string or a {Buffer}.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 ```mjs
 import { appendFile } from 'fs';
 
@@ -4081,6 +4090,9 @@ a file descriptor.
 
 The `encoding` option is ignored if `data` is a buffer.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 If `data` is a plain object, it must have an own (not inherited) `toString`
 function property.
 
@@ -4255,6 +4267,9 @@ changes:
 Synchronously append data to a file, creating the file if it does not yet
 exist. `data` can be a string or a {Buffer}.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 ```mjs
 import { appendFileSync } from 'fs';
 
@@ -5211,6 +5226,9 @@ Returns `undefined`.
 If `data` is a plain object, it must have an own (not inherited) `toString`
 function property.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 For detailed information, see the documentation of the asynchronous version of
 this API: [`fs.writeFile()`][].