update File.ReadAllText supported encoding in the remarks (#8562)

Author: eriawan

xml/System.IO/File.xml

@@ -4388,7 +4388,7 @@ The following example moves a file.
 ## Remarks
  This method opens a file, reads all the text in the file, and returns it as a string. It then closes the file.
 
- This method attempts to automatically detect the encoding of a file based on the presence of byte order marks. Encoding formats UTF-8 and UTF-32 (both big-endian and little-endian) can be detected.
+ This method attempts to automatically detect the encoding of a file based on the presence of byte order marks. It automatically recognizes UTF-8, little-endian UTF-16, big-endian UTF-16, little-endian UTF-32, and big-endian UTF-32 text if the file starts with the appropriate byte order marks.
 
  Use the <xref:System.IO.File.ReadAllText%28System.String%2CSystem.Text.Encoding%29> method overload when reading files that might contain imported text, because unrecognized characters may not be read correctly.
 
@@ -4492,7 +4492,7 @@ The following example moves a file.
 ## Remarks
  This method opens a file, reads all the text in the file, and returns it as a string. It then closes the file.
 
- This method attempts to automatically detect the encoding of a file based on the presence of byte order marks. Encoding formats UTF-8 and UTF-32 (both big-endian and little-endian) can be detected.
+ This method attempts to automatically detect the encoding of a file based on the presence of byte order marks. It automatically recognizes UTF-8, little-endian UTF-16, big-endian UTF-16, little-endian UTF-32, and big-endian UTF-32 text if the file starts with the appropriate byte order marks.
 
  The file handle is guaranteed to be closed by this method, even if exceptions are raised.