Clarify that the URL scheme does not include the ':'

From the documentation of setScheme it was not clear if the scheme should
be terminated by a ':' or not. Documentation has been updated to clarify
the expected syntax for the scheme.

Change-Id: Ied8533beef7daa12e1d5e7da0649c184efb84522
Reviewed-by: David Faure <david.faure@kdab.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qurl.cpp

@@ -1840,12 +1840,21 @@ void QUrl::setUrl(const QString &url, ParsingMode parsingMode)
     input. It must also start with an ASCII letter.
 
     The scheme describes the type (or protocol) of the URL. It's
-    represented by one or more ASCII characters at the start the URL,
-    and is followed by a ':'. The following example shows a URL where
-    the scheme is "ftp":
+    represented by one or more ASCII characters at the start the URL.
+
+    A scheme is strictly \l {http://www.ietf.org/rfc/rfc3986.txt} {RFC 3986}-compliant:
+        \tt {scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )}
+
+    The following example shows a URL where the scheme is "ftp":
 
     \image qurl-authority2.png
 
+    To set the scheme, the following call is used:
+    \code
+        QUrl url;
+        url.setScheme("ftp");
+    \endcode
+
     The scheme can also be empty, in which case the URL is interpreted
     as relative.
 
@@ -3327,7 +3336,7 @@ QString QUrl::fromPercentEncoding(const QByteArray &input)
     them to \a include.
 
     Unreserved is defined as:
-       ALPHA / DIGIT / "-" / "." / "_" / "~"
+       \tt {ALPHA / DIGIT / "-" / "." / "_" / "~"}
 
     \snippet code/src_corelib_io_qurl.cpp 6
 */