document newline normalization in literal strings (#14073)

(cherry picked from commit 9ac2fd5)
ref #14078

doc/manual/strings.rst

@@ -441,8 +441,8 @@ backslash:
     julia> print("I have \$100 in my account.\n")
     I have $100 in my account.
 
-Triple-Quoted Strings Literals
-------------------------------
+Triple-Quoted String Literals
+-----------------------------
 
 When strings are created using triple-quotes (``"""..."""``) they have some
 special behavior that can be useful for creating longer blocks of text. First,
@@ -484,6 +484,12 @@ defining strings within code that is indented. For example:
 In this case the final (empty) line before the closing ``"""`` sets the
 indentation level.
 
+Note that line breaks in literal strings, whether single- or triple-quoted,
+result in a newline (LF) character ``\n`` in the string, even if your
+editor uses a carriage return ``\r`` (CR) or CRLF combination to end lines.
+To include a CR in a string, use an explicit escape ``\r``; for example,
+you can enter the literal string ``"a CRLF line ending\r\n"``.
+
 Common Operations
 -----------------