Fix description of 'emacs-internal'

* doc/lispref/nonascii.texi (Coding System Basics): Correct
inaccuracy in description of 'emacs-internal'.  (Bug#29916)

doc/lispref/nonascii.texi

@@ -1112,7 +1112,9 @@ represented in the internal Emacs encoding (@pxref{Text
 Representations}).  This is like @code{raw-text} in that no code
 conversion happens, but different in that the result is multibyte
 data.  The name @code{emacs-internal} is an alias for
-@code{utf-8-emacs}.
+@code{utf-8-emacs-unix} (so it forces no conversion of end-of-line,
+unlike @code{utf-8-emacs}, which can decode all 3 kinds of
+end-of-line conventions).
 
 @defun coding-system-get coding-system property
 This function returns the specified property of the coding system