#161966929 Implement article read time

What does this PR do?

Implement the article read time feature

Description of Task to be completed

Estimate the amount of time it takes to read an article

How should this be manually tested?

git clone -b ft-article-read-time-161966929 https://github.com/andela/ah-infinity-stones and cd ah-infinity-stones.
Run python3 -m venv virtual to create a virtual environment and source virtual/bin/activate to activate it.
pip install -r requirements.txt to install dependencies
Create a test database in the postgres shell

Set up environment variables using the sample below as a guide:

export DATABASE_PASSWORD='<postgres user's password>'
export HOST='localhost'
export PORT='5432'
export DATABASE_NAME='<name_of_database>' 
export SECRET_KEY='<personal_secret_key>'
export EMAIL_HOST_USER='<email_host_username>'
export EMAIL_HOST_PASSWORD='<email_host_password>'

Run python3 manage.py makemigrations followed by python3 manage.py migrate to apply migrations Acess http://127.0.0.1:8000/api/users/ through Postman, provide inputs in the following format and create account.
```
{
"user": {
    "username": "remmykn",
    "email": "remmy@test.com",
    "password": "Password@123"
}
}
```


Check your email and activate the account. Use the registration token to access the following endpoints:
- `http://127.0.0.1:8000/api/articles` - to post an article 

### Relevant pivotal tracker stories
[Delivers #161966929](https://www.pivotaltracker.com/story/show/161966929)

### Screenshots
![image](https://user-images.githubusercontent.com/17976289/50178944-ddfcb200-0316-11e9-904c-14f63c15fcce.png)
![image](https://user-images.githubusercontent.com/17976289/50178969-ef45be80-0316-11e9-90af-1850977ab8b4.png)

andela / ah-infinity-stones

#161966929 Implement article read time #43

What does this PR do?

Description of Task to be completed

How should this be manually tested?