Mention the CR vs. LF problem in the documentation

Let's hope that this will help to avoid that people run into the same
problem again in the future. At least we've got some lines of documentation
this way where we can point people to who try to use "nc" in the wrong way.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

README

diff --git a/README b/README
index 2944588..a06d2d8 100644
--- a/README
+++ b/README
@@ -266,6 +266,20 @@
 guidelines for the Linux kernel [4], i.e. indent with tabs, not with spaces.
 
 
+6.0 Tips and tricks
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+- Note that the serial console support is written with serial terminals in
+  mind. Thus SLOF only looks for CR (0x0d) characters as line endings at the
+  command prompt. If you want to connect to the console with a program like
+  "ncat" for example, you have to make sure that it indeed sends CR characters
+  instead of plain LF (0x0a) characters. For ncat that means that you have to
+  use "nc -C ..." to enable the CR-LF mode, or even better, switch the terminal
+  to raw mode instead, for example like this:
+
+    stty raw -echo ; nc -U /path/to/chardev-socket-from-qemu ; stty sane
+
+
 Documentation
 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++