Update README (for ONBOARD directices)

the README was not explicit on how to add system package priori to execute the
docker directives imposing the requirements.txt

Issue-ID: INT-1589

Signed-off-by: mrichomme <morgan.richomme@orange.com>
Change-Id: I657b737b5d0fe6a3a7d3fd1e61ffe94571e7e857
Signed-off-by: mrichomme <morgan.richomme@orange.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/README.md b/README.md
index 0f12c70..ecea579 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,38 @@ FROM nexus3.onap.org:10001/onap/integration-python
 RUN echo "Add your specifc docker needs here."
 ```
 
+Note if you need to specific package to build python library, it is possible.
+You need to use root user temporarily as described hereafter.
+ONBUILD directives will be called after the root section, allowing you to install
+the system packages you need to execute your pip install -rrequirements.txt.
+
+```
+FROM nexus3.onap.org:10001/onap/integration-python:7.0.0
+
+USER root
+
+# Needed for pycurl
+# Install packages only needed for building
+RUN apk update && \
+    apk add binutils jq libpng && \
+    apk add --no-cache --virtual .build-dependencies \
+        libressl-dev && \
+    apk del .build-dependencies
+
+# user/group are the same as in integration/docker/onap-python base image
+ENV user=onap group=onap
+
+USER $user
+```
+
+Please note that you are responsible of the licenses of the packages you are adding.
+Only the baseline image is GPLv3 free.
+For example be aware that bash is GPLv3.
+
+See SDC full example in [3].
+
 [1]: http://wiki.onap.org
 
 [2]: https://wiki.onap.org/display/DW/Database%2C+Java%2C+Python%2C+Docker%2C+Kubernetes%2C+and+Image+Versions
+
+[3]: https://gerrit.onap.org/r/gitweb?p=sdc/sdc-docker-base.git;a=blob;f=base_sdc-python/Dockerfile;h=57daaa9621e1af122b7c5941f3733db743bbe6d5;hb=0e0dff07cf70588ef270e12e5ec43805c12daa4d