Added cd to bitcoin-spv setup instruction
2. Configure environment variable with a path to the cloned repository, e.g.:
```sh
- export BITCOIN_SPV_DIR="~/workspace/bitcoin-spv"
+ export BITCOIN_SPV_DIR="/Users/jakub/workspace/bitcoin-spv/"
```
3. Install python 3.6.6:
4. Set up python environment:
```sh
brew install pipenv
- pipenv install --python ~/.pyenv/versions/3.6.6/bin/python
+ cd $BITCOIN_SPV_DIR && pipenv install --python ~/.pyenv/versions/3.6.6/bin/python
```
5. Compile contracts
```sh
+ cd $BITCOIN_SPV_DIR
npm install
npm run compile
```
