install doc

docs/source/install/index.rst

 Install DGL
 ============
 
-TBD: installation instructions
+At this stage, we recommend installing DGL from source. To quickly try out DGL and its demo/tutorials, checkout `Install from docker`_.
+
+Get source codes
+----------------
+First, download the source files from github. Note you need to use the ``--recursive`` option to
+also clone the submodules.
+
+.. code:: bash
+
+    git clone --recursive https://github.com/jermainewang/dgl.git
+
+You can also clone the repository first and type following commands:
+
+.. code:: bash
+
+    git submodule init
+    git submodule update
+
+
+Build shared library
+--------------------
+Before building the library, please make sure the following dependencies are installed
+(use ubuntu as an example):
+
+.. code:: bash
+
+    sudo apt-get update
+    sudo apt-get install -y python
+
+We use cmake (minimal version 2.8) to build the library.
+
+.. code:: bash
+
+    mkdir build
+    cd build
+    cmake ..
+    make -j4
+
+Build python binding
+--------------------
+DGL's python binding depends on following packages (tested version):
+
+* numpy (>= 1.14.0)
+* scipy (>= 1.1.0)
+* networkx (>= 2.1)
+
+To install them, use following command:
+
+.. code:: bash
+
+    pip install --user numpy scipy networkx
+
+There are several ways to setup DGL's python binding. We recommend developers at the current stage
+use environment variables to find python packages.
+
+.. code:: bash
+
+    export DGL_HOME=/path/to/dgl
+    export PYTHONPATH=$DGL_HOME$/python:${PYTHONPATH}
+    export DGL_LIBRARY_PATH=$DGL_HOME$/build
+
+The ``DGL_LIBRARY_PATH`` variable is used for our python package to locate the shared library
+built above. Use following command to test whether the installation is successful or not.
+
+.. code:: bash
+
+    python -c 'import dgl'
+
+Install from docker
+-------------------
+TBD

python/dgl/batched_graph.py

@@ -76,15 +76,15 @@ class BatchedDGLGraph(DGLGraph):
 
     # override APIs
     def add_nodes(self, num, reprs=None):
-        """Add nodes."""
+        """Add nodes. Disabled because BatchedDGLGraph is read-only."""
         raise RuntimeError('Readonly graph. Mutation is not allowed.')
 
     def add_edge(self, u, v, reprs=None):
-        """Add one edge."""
+        """Add one edge. Disabled because BatchedDGLGraph is read-only."""
         raise RuntimeError('Readonly graph. Mutation is not allowed.')
 
     def add_edges(self, u, v, reprs=None):
-        """Add many edges."""
+        """Add many edges. Disabled because BatchedDGLGraph is read-only."""
         raise RuntimeError('Readonly graph. Mutation is not allowed.')
 
     # new APIs