LDAP for docker instructions

Dear Redashers,

this instructions regarding the extension of docker images to support ldap published here:
https://redash.io/help/open-source/admin-guide/ldap-authentication

In my understanding should be amended as:

FROM redash/redash:latest

USER root
RUN pip install --upgrade pip #<- optional
RUN pip install ldap3
USER redash

Best
M