Explain the use of charset parameter with Content-Type header. Issue11082
diff --git a/Doc/library/urllib.parse.rst b/Doc/library/urllib.parse.rst
index aece714..b33e8fe 100644
--- a/Doc/library/urllib.parse.rst
+++ b/Doc/library/urllib.parse.rst
@@ -512,9 +512,10 @@
Convert a mapping object or a sequence of two-element tuples, which may
either be a :class:`str` or a :class:`bytes`, to a "percent-encoded"
- string. The resultant string must be converted to bytes using the
- user-specified encoding before it is sent to :func:`urlopen` as the optional
- *data* argument.
+ string. If the resultant string is to be used as a *data* for POST
+ operation with :func:`urlopen` function, then it should be properly encoded
+ to bytes, otherwise it would result in a :exc:`TypeError`.
+
The resulting string is a series of ``key=value`` pairs separated by ``'&'``
characters, where both *key* and *value* are quoted using :func:`quote_plus`
above. When a sequence of two-element tuples is used as the *query*