[docs] pip install packages in order for dependencies

docs/installation.md

@@ -59,7 +59,7 @@ The main requirements are `numpy` and `boost.python` (provided by boost). `panda
 
 You can install the dependencies with
 
-    pip install -r /path/to/caffe/python/requirements.txt
+    cat caffe/python/requirements.txt | xargs pip install
 
 but we highly recommend first installing the [Anaconda](https://store.continuum.io/cshop/anaconda/) Python distribution, which provides most of the necessary packages, as well as the `hdf5` library dependency.
 

python/requirements.txt

@@ -8,6 +8,7 @@ nose>=1.3.0
 numpy>=1.7.1
 pandas>=0.12.0
 protobuf>=2.5.0
+python-dateutil>=1.4,<2
 python-gflags>=2.0
 scikit-image>=0.9.3
 scikit-learn>=0.14.1