Rollup merge of #129718 - lolbinarycat:remove_dir-docs, r=Noratrieb

add guarantee about remove_dir and remove_file error kinds

approved in ACP https://github.com/rust-lang/libs-team/issues/433

library/std/src/fs.rs

@@ -1991,6 +1991,11 @@ fn as_inner(&self) -> &fs_imp::DirEntry {
 /// * The file doesn't exist.
 /// * The user lacks permissions to remove the file.
 ///
+/// This function will only ever return an error of kind `NotFound` if the given
+/// path does not exist. Note that the inverse is not true,
+/// ie. if a path does not exist, its removal may fail for a number of reasons,
+/// such as insufficient permissions.
+///
 /// # Examples
 ///
 /// ```no_run
@@ -2448,6 +2453,11 @@ pub fn create_dir_all<P: AsRef<Path>>(path: P) -> io::Result<()> {
 /// * The user lacks permissions to remove the directory at the provided `path`.
 /// * The directory isn't empty.
 ///
+/// This function will only ever return an error of kind `NotFound` if the given
+/// path does not exist. Note that the inverse is not true,
+/// ie. if a path does not exist, its removal may fail for a number of reasons,
+/// such as insufficient permissions.
+///
 /// # Examples
 ///
 /// ```no_run