add installation note to README.md
`jiant` is a software toolkit for natural language processing research, designed to facilitate work on multitask learning and transfer learning for sentence understanding tasks.
+### Installation
+```
+git clone https://github.com/jiant-dev/jiant.git
+pip install -r jiant/requirements-dev.txt
+```
+You can confirm that `jiant` is installed by running a basic experiment using the instructions [here](./examples/guides/quick_start_cli.md).
+
### Getting started
Examples to help you get started can be found here [here](./examples/README.md).
