docs:Improve the README of vpp docs

Type:fix

Change-Id: Ie2ae728450ef123379b697cdf9c873d5bec01b47
Signed-off-by: yanlong <dyl_wlc@163.com>

docs/README

@@ -1,49 +1,2 @@
-
-Building VPP Documents
-
-These instructions show how the VPP documentation sources are built.
-
-To build your files, you can either Create a Virtual Environment using
-virtualenv, which installs all the required applications for you.
-
-Create a Virtual Environment using virtualenv
-============================
-
-For more information on how to use the Python virtual environment check
-out https://packaging.python.org/guides/installing-using-pip-and-virtualenv
-
-Get the Documents
-------------------------------
-
-For example start with a clone of the vpp.
-
-$ git clone https://gerrit.fd.io/r/vpp
-$ cd vpp
-
-Install the virtual environment
-----------------------------------------------
-
-$ python -m pip install --user virtualenv
-$ python -m virtualenv env
-$ source env/bin/activate
-$ pip install -r docs/etc/requirements.txt
-$ cd docs
-
-Which installs all the required applications into it's own, isolated,
-virtual environment, so as to not interfere with other builds that may
-use different versions of software.
-
-Build the html files
-----------------------------
-
-Be sure you are in your vpp/docs directory, since that is where Sphinx will
-look for your conf.py file, and build the documents into an index.html file
-
-$ make html
-
-View the results
-------------------------
-
-If there are no errors during the build process, you should now have an
-index.html file in your vpp/docs/_build/html directory, which you can
-then view in your browser.
+If you want to build a VPP documentation source, please refer to the VPP user documentation:
+https://fd.io/docs/vpp/master/contributing/writingdocs.html