message: [install doc] various tweaks
  * various tweaks
  expanding on some things after having difficulties and getting answers.
  * typos
  * typos
  * Minor updates
diff: @@ -17,18 +17,25 @@ Note: all Python dependencies will be automatically installed if install the Fle
  ## 2.1 Makefile
  ### Build dependent libraries
  -* Build the NCCL library. (If using NCCL for parameter synchornization.)
  +* Build the NCCL library. (If using NCCL for parameter synchronization. )
  ```
  cd nccl
  make -j src.build NVCC_GENCODE="-gencode=arch=compute_XX,code=sm_XX"
  ```
  -Replace XX with the compatability of your GPU devices (e.g., 70 for Volta GPUs and 60 for Pascal GPUs).
  +Replace XX with the compatibility of your GPU devices (e.g., 70 for Volta GPUs and 60 for Pascal GPUs).
  +
  +But you could also install it via `apt` if your system supports it:
  +```
  +sudo apt install libnccl-dev
  +```
  ### Build FlexFlow runtime with C++ interface
  The `FF_HOME` environment variable is used for building and running FlexFlow. You can add the following line in `~/.bashrc`.
  ```
  export FF_HOME=/path/to/FlexFlow
  ```
  +The path should point to where you cloned this repository.
  +
  Use the following command line to build a DNN model (e.g., InceptionV3). See the [examples](examples) folders for more existing FlexFlow applications.
  ```
  ./ffcompile.sh examples/InceptionV3
  @@ -36,15 +43,21 @@ Use the following command line to build a DNN model (e.g., InceptionV3). See the
  ### Build FlexFlow Runtime with Python Interface (C++ interface is also enabled)
  -* Set the following enviroment variables. For `CUDNN_HOME`, you should be able to find `cudnn.h` under `CUDNN_HOME/include` and `libcudnn.so` under `CUDNN_HOME/lib` or `CUDNN_HOME/lib64`.
  +* Set the following environment variables. For `CUDNN_HOME`, you should be able to find `cudnn.h` under `CUDNN_HOME/include` and `libcudnn.so` under `CUDNN_HOME/lib` or `CUDNN_HOME/lib64`.
  ```
  export FF_HOME=/path/to/FlexFlow
  export CUDNN_HOME=/path/to/cudnn
  ```
  -To expedite the compilation, you can also set the `GPU_ARCH` enviroment variable to be the compatability of your GPU devices (e.g., 70 for Volta GPUs and 60 for Pascal GPUs).
  +To expedite the compilation, you can also set the `GPU_ARCH` environment variable to be the compatibility of your GPU devices (e.g., 70 for Volta GPUs and 60 for Pascal GPUs).
  ```
  export GPU_ARCH=your_gpu_arch
  ```
  +If you have different cards, pass them all via comma, e.g.:
  +
  +```
  +export GPU_ARCH=70,86
  +```
  +
  If Legion can not automatically detect your Python installation, you need to tell Legion manually by setting the `PYTHON_EXE`, `PYTHON_LIB` and `PYTHON_VERSION_MAJOR`, please refer to the `python/Makefile` for details
  * Build the flexflow python executable using the following command line
  @@ -62,7 +75,7 @@ mkdir build
  cd build
  cmake ../ -DCUDA_ARCH=xx -DPYTHON_VERSION=3.x (replace the xx with the corrected number)
  make
  -make install
  +sudo make install
  ```
  Note: CMake sometimes can not automatically detect the correct `CUDA_ARCH`, so please set `CUDA_ARCH` if CMake can not detect it.
  