add env installation

README.md

+# Installation
+
+- `conda create --name py36-tf1 python=3.6 tensorflow-gpu=1.15`
+- `conda activate py36-tf1`
+- `conda install -c conda-forge opencv`
+- `pip install -r requirements.txt`
+
 # COVID-Net Open Source Initiative
 
 **Note: The COVID-Net models provided here are intended to be used as reference models that can be built upon and enhanced as new data becomes available. They are currently at a research stage and not yet intended as production-ready models (not meant for direct clinical diagnosis), and we are working continuously to improve them as new data becomes available. Please do not use COVID-Net for self-diagnosis and seek help from your local health authorities.**