add mnist to travis.yml tutorial

hw4-gradient-descent/add_mnist_to_travis.md

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+## Adding MNIST to .travis.yml  
+
+
+For this homework, your are required to download the ```MNIST dataset``` in order to pass all the tests locally.
+
+However, since you should not push the ```MNIST dataset``` to your git repo, the tests on ```travis``` will never pass.
+
+Here is a small tutorial on how to add ```MNIST dataset``` to your ```travis``` to get the green checkmark for your repo:)
+
+
+You can do it by simply adding the following commands in your ```.travis.yml``` file after the line ```pip install -r requirements.txt```:
+
+```
+- cd data
+- wget -c http://yann.lecun.com/exdb/mnist/train-images-idx3-ubyte.gz
+- wget -c http://yann.lecun.com/exdb/mnist/train-labels-idx1-ubyte.gz
+- wget -c http://yann.lecun.com/exdb/mnist/t10k-images-idx3-ubyte.gz
+- wget -c http://yann.lecun.com/exdb/mnist/t10k-labels-idx1-ubyte.gz
+- gzip -d train-images-idx3-ubyte.gz
+- gzip -d train-labels-idx1-ubyte.gz
+- gzip -d t10k-images-idx3-ubyte.gz
+- gzip -d t10k-labels-idx1-ubyte.gz
+- cd ..
+```
+
+These commands enter your data directory, download the MNIST dataset, and unzip the files. It might take longer than usual for it to build since downloading MNIST could be slow.
+
+</br>
+</br>
+
+For your convenience, here is what my entire ```.travis.yml``` looks like for this homework:
+```
+# what language the build will be configured for
+language: python
+
+# specify what versions of python will be used
+python:
+    - 3.8
+
+# what branches should be evaluated
+branches:
+    only:
+        - master
+
+# list of commands to run to setup the environment
+install:
+      - sudo apt-get update
+      # We do this conditionally because it saves us some downloading if the
+      # version is the same.
+      - if [[ "$TRAVIS_PYTHON_VERSION" == "2.7" ]]; then
+          wget https://repo.continuum.io/miniconda/Miniconda2-latest-Linux-x86_64.sh -O miniconda.sh;
+        else
+          wget https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh -O miniconda.sh;
+        fi
+      - bash miniconda.sh -b -p $HOME/miniconda
+      - source "$HOME/miniconda/etc/profile.d/conda.sh"
+      - hash -r
+      - conda config --set always_yes yes --set changeps1 no
+      - conda update -q conda
+      # Useful for debugging any issues with conda
+      - conda info -a
+
+      # Enlist your dependencies
+      - conda create -q -n test-environment python=$TRAVIS_PYTHON_VERSION 
+      - conda activate test-environment
+      - pip install -r requirements.txt
+      - cd data
+      - wget -c http://yann.lecun.com/exdb/mnist/train-images-idx3-ubyte.gz
+      - wget -c http://yann.lecun.com/exdb/mnist/train-labels-idx1-ubyte.gz
+      - wget -c http://yann.lecun.com/exdb/mnist/t10k-images-idx3-ubyte.gz
+      - wget -c http://yann.lecun.com/exdb/mnist/t10k-labels-idx1-ubyte.gz
+      - gzip -d train-images-idx3-ubyte.gz
+      - gzip -d train-labels-idx1-ubyte.gz
+      - gzip -d t10k-images-idx3-ubyte.gz
+      - gzip -d t10k-labels-idx1-ubyte.gz
+      - cd ..
+
+# the actual commands to run
+script:
+    - python -m pytest -s
+```
+