Add explaination of backslash in typography

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@8579 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

prologue/typography.xml

@@ -21,6 +21,19 @@
   otherwise noted in the surrounding text. It is also used in the explanation
   sections to identify which of the commands is being referenced.</para>
 
+  <para>In some cases, a logical line is extended to two or more physical lines
+  with a backslash at the end of the line.</para>
+
+<screen role="nodump"><userinput>CC="gcc -B/usr/bin/" ../binutils-2.18/configure \
+  --prefix=/tools --disable-nls --disable-werror</userinput></screen>
+
+  <para>Note that the backslash must be followed by an immediate return.  Other
+  whitespace charaters like spaces or tab characters will create incorrect
+  results.</para>
+
+
+
+
 <screen><computeroutput>install-info: unknown option '--dir-file=/mnt/lfs/usr/info/dir'</computeroutput></screen>
 
   <para>This form of text (fixed-width text) shows screen output, probably as