doc for multiline input in sagecommandline

resolves a part of #38

Author: dimpase

sagetex.dtx

@@ -818,20 +818,26 @@ suggestions.
 % provides Python syntax highlighting and line numbers. For example,
 % \begin{quote}
 % |\begin{sagecommandline}|\\
-% |  sage: 1+1|\\
-% |  2|\\
+% |  sage: t = 1+1|\\
+% |  sage: for i in range(101): # multiline input example|\\
+% |  ....:     t+=1|\\
+% |  sage: t|\\
+% |  103|\\
 % |  sage: factor(x^2 + 2*x + 1)|\\
 % |\end{sagecommandline}|
 % \end{quote}
 % becomes
 \begin{sagecommandline}
-  sage: 1+1
-  2
+  sage: t = 1+1
+  sage: for i in range(101): # multiline input example
+  ....:     t+=1
+  sage: t
+  103
   sage: factor(x^2 + 2*x + 1)
 \end{sagecommandline}
 % You have a choice of either explicitly providing the Sage output or
 % leaving it up to the computer to fill in the blanks. Above, the output
-% for $1+1$ was provided, but the output for the |factor()| command
+% for $t$ was provided, but the output for the |factor()| command
 % wasn't. Moreover, any Sage comment that starts with a ``at'' sign is
 % escaped to \LTX. In particular, you can use |\label| to mark line
 % numbers in order to |\ref|erence and |\pageref|erence them as usual.