Fix Docker invocation (#300)

* fix syntax error in Dockerfile

* fix Docker invocation

It makes no sense to pass the `-t` argument twice and we need to tell
Docker where to find the Dockerfile. Also, it makes sense to write the
config file in a standard location. In my tests, I also had to create
the directory by hand otherwise I got this error:

    cdparanoia can defeat the audio cache on this drive.
    Adding drive cache behaviour to configuration file.
    Traceback (most recent call last):
      File "/usr/local/bin/whipper", line 11, in <module>
        load_entry_point('whipper==0.7.0', 'console_scripts', 'whipper')()
      File "/usr/local/lib/python2.7/dist-packages/whipper-0.7.0-py2.7.egg/whipper/command/main.py", line 36, in main
        ret = cmd.do()
      File "/usr/local/lib/python2.7/dist-packages/whipper-0.7.0-py2.7.egg/whipper/command/basecommand.py", line 139, in do
        return self.cmd.do()
      File "/usr/local/lib/python2.7/dist-packages/whipper-0.7.0-py2.7.egg/whipper/command/basecommand.py", line 139, in do
        return self.cmd.do()
      File "/usr/local/lib/python2.7/dist-packages/whipper-0.7.0-py2.7.egg/whipper/command/drive.py", line 63, in do
        info[0], info[1], info[2], t.defeatsCache)
      File "/usr/local/lib/python2.7/dist-packages/whipper-0.7.0-py2.7.egg/whipper/common/config.py", line 115, in setDefeatsCache
        section = self._findOrCreateDriveSection(vendor, model, release)
      File "/usr/local/lib/python2.7/dist-packages/whipper-0.7.0-py2.7.egg/whipper/common/config.py", line 164, in _findOrCreateDriveSection
        self.write()
      File "/usr/local/lib/python2.7/dist-packages/whipper-0.7.0-py2.7.egg/whipper/common/config.py", line 58, in write
        shutil.move(path, self._path)
      File "/usr/lib/python2.7/shutil.py", line 316, in move
        copy2(src, real_dst)
      File "/usr/lib/python2.7/shutil.py", line 144, in copy2
        copyfile(src, dst)
      File "/usr/lib/python2.7/shutil.py", line 97, in copyfile
        with open(dst, 'wb') as fdst:
    IOError: [Errno 13] Permission denied: u'/home/worker/.config/whipper/whipper.conf'

* remove needless tag version

:latest is implicit so it's useless noise as well.

* Update README.md

Dockerfile

@@ -34,7 +34,7 @@ RUN mkdir /whipper
 COPY . /whipper/
 RUN cd /whipper/src && make && make install \
   && cd /whipper && python2 setup.py install \
-  && rm -rf /whipper
+  && rm -rf /whipper \
   && whipper -v
 
 # add user

README.md

@@ -72,18 +72,22 @@ Whipper still isn't available as an official package in every Linux distribution
 
 You can easily install whipper by making use of the included Dockerfile without needing to care about the required dependencies:
 
-`docker build -t whipper/whipper:0.7-git -t whipper/whipper:latest`
+`docker build -t whipper/whipper`
 
 It's recommended to create an alias for a convenient usage:
 
 ```bash
 alias whipper="docker run -ti --rm --device=/dev/cdrom \
-    -v ${PWD}/config:/home/worker/.config/whipper \
+    -v ~/.config/whipper:/home/worker/.config/whipper \
     -v ${PWD}/output:/output \
     whipper/whipper"
 ```
 
-You should put this e.g. into your `.bash_aliases`. Also keep in mind to substitude the path definitions to something that fits to your needs (e.g. replace `… -v ${PWD}/output:/output …` with `… -v ${HOME}/ripped:/output \ …`).
+You should put this e.g. into your `.bash_aliases`. Also keep in mind to substitute the path definitions to something that fits to your needs (e.g. replace `… -v ${PWD}/output:/output …` with `… -v ${HOME}/ripped:/output \ …`).
+
+Make sure you create the configuration directory:
+
+`mkdir -p ~/.config/whipper ${PWD}/output`
 
 Finally you can test the correct installation: