Add simple readme about what it is

README.rst

+=======================================================================
+ Helloweb - simple demo to say hello to the Web in different languages
+=======================================================================
+
+All programs implement simple Web-server which listens on an IPv6 address and
+answers HTTP requests with simple "Hello" message.
+
+The programs are used in SlapOS helloworld_ software release.
+
+The following languages are demonstrated:
+
+- Python
+
+.. _helloworld: https://lab.nexedi.com/nexedi/slapos/tree/master/software/helloworld