Update README, dependencies and supporting files for cover art feature

Signed-off-by: ABCbum <kimlong221002@gmail.com>
Co-authored-by: JoeLametta <JoeLametta@users.noreply.github.com>
Signed-off-by: JoeLametta <JoeLametta@users.noreply.github.com>

.travis.yml

@@ -24,7 +24,7 @@ install:
     # Dependencies
     - sudo apt-get -qq update
     - pip install --upgrade -qq pip
-    - sudo apt-get -qq install cdparanoia cdrdao flac gir1.2-glib-2.0 libcdio-dev libgirepository1.0-dev libiso9660-dev libsndfile1-dev sox swig libcdio-utils libdiscid0
+    - sudo apt-get -qq install cdparanoia cdrdao flac gir1.2-glib-2.0 libcdio-dev libgirepository1.0-dev libiso9660-dev libsndfile1-dev sox swig libcdio-utils libdiscid0 python3-pil
     # newer version of pydcio requires newer version of libcdio than travis has
     - pip install pycdio==0.21
     # install rest of dependencies

Dockerfile

@@ -21,6 +21,7 @@ RUN apt-get update && apt-get install --no-install-recommends -y \
     python3-gi \
     python3-musicbrainzngs \
     python3-mutagen \
+    python3-pil \
     python3-pip \
     python3-requests \
     python3-ruamel.yaml \

README.md

@@ -155,6 +155,13 @@ PyPI installable dependencies are listed in the [requirements.txt](https://githu
 
 `pip install -r requirements.txt`
 
+### Optional dependencies
+- [pillow](https://pypi.org/project/Pillow/), for completely supporting the cover art feature (`embed` and `complete` option values won't work otherwise).
+
+This dependency isn't listed in the `requirements.txt`, to install it just issue the following command:
+
+`pip install Pillow`
+
 ### Fetching the source code
 
 Change to a directory where you want to put whipper source code (for example, `$HOME/dev/ext` or `$HOME/prefix/src`)

setup.py

@@ -16,6 +16,9 @@ setup(
                   libraries=['sndfile'],
                   sources=['src/accuraterip-checksum.c'])
     ],
+    extras_require={
+        'cover_art': ["pillow"]
+    },
     entry_points={
         'console_scripts': [
             'whipper = whipper.command.main:main'