Improve the String tutorial docs (GH-4541)

The paragraph that contains example of string literal concatenation was placed
after the section about concatenation using the '+' sign.
Moved the paragraph to the appropriate section.

Doc/tutorial/introduction.rst

@@ -212,6 +212,13 @@ to each other are automatically concatenated. ::
    >>> 'Py' 'thon'
    'Python'
 
+This feature is particularly useful when you want to break long strings::
+
+   >>> text = ('Put several strings within parentheses '
+   ...         'to have them joined together.')
+   >>> text
+   'Put several strings within parentheses to have them joined together.'
+
 This only works with two literals though, not with variables or expressions::
 
    >>> prefix = 'Py'
@@ -227,13 +234,6 @@ If you want to concatenate variables or a variable and a literal, use ``+``::
    >>> prefix + 'thon'
    'Python'
 
-This feature is particularly useful when you want to break long strings::
-
-   >>> text = ('Put several strings within parentheses '
-   ...         'to have them joined together.')
-   >>> text
-   'Put several strings within parentheses to have them joined together.'
-
 Strings can be *indexed* (subscripted), with the first character having index 0.
 There is no separate character type; a character is simply a string of size
 one::