django: add README (#7181)

plugins/django/README.md

+# Django plugin
+
+This plugin adds completion and hints for the [Django Project](https://www.djangoproject.com/) `manage.py` commands
+and options.
+
+To use it, add `django` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... django)
+```
+
+## Usage
+
+```zsh
+$> python manage.py (press <TAB> here)
+```
+
+Would result in:
+
+```zsh
+cleanup                    -- remove old data from the database
+compilemessages            -- compile .po files to .mo for use with gettext
+createcachetable           -- creates table for SQL cache backend
+createsuperuser            -- create a superuser
+dbshell                    -- run command-line client for the current database
+diffsettings               -- display differences between the current settings and Django defaults
+dumpdata                   -- output contents of database as a fixture
+flush                      -- execute 'sqlflush' on the current database
+inspectdb                  -- output Django model module for tables in database
+loaddata                   -- install the named fixture(s) in the database
+makemessages               -- pull out all strings marked for translation
+reset                      -- executes 'sqlreset' for the given app(s)
+runfcgi                    -- run this project as a fastcgi
+runserver                  -- start a lightweight web server for development
+...
+```
+
+If you want to see the options available for a specific command, try:
+
+```zsh
+$> python manage.py makemessages (press <TAB> here)
+```
+
+And that would result in:
+
+```zsh
+--all         -a  -- re-examine all code and templates
+--domain      -d  -- domain of the message files (default: "django")
+--extensions  -e  -- file extension(s) to examine (default: ".html")
+--help            -- display help information
+--locale      -l  -- locale to process (default: all)
+--pythonpath      -- directory to add to the Python path
+--settings        -- python path to settings module
+...
+```
+