Updated the README.md, added notebook and visualizations

[mitchdolby]

No description provided.

[chendaniely]

@mitchdolby I noticed from #43 that you are loading datasets that aren't documented in this repository. please also add the code you used to pull the datasets down.

[chendaniely]

@mitchdolby Notes about your code:

if you want to add a missing value, do not use the string "NaN", juse the nan, NAN, or NaN values from the numpy library.

To check if a value is missing you can use the pd.isnull function. Do not use == or != to check on a string. Missing values are not equal to anything, e.g., NaN == NaN is False and NaN != NaN is True

[chendaniely]

• Fix data files

• move png images, they are in the notebook in the cell output, but no code was used to explicitely save them to file.

• Fix NaN code

When merged this PR fixes #33

[mitchdolby]

link to data: https://aqicn.org/data-platform/register/

[chendaniely]

Data Usage Statement

The data platform observational data are not fully verified or validated; these data are subject to change, error, and correction. The data and information are in no way official.
The data platform observational data can not be used for any official comparison, ranking, report or data analysis. The official and validated data must be obtained directly from the originating EPA.
If observational data are used for analyses, displayed on web pages, or used for other programs or products, the analysis results, displays, or products must indicate that these data are not fully verified or validated. 

Publications, analyses, products, presentations, and/or derived information that rely on these data must give attribution to the originating EPA (Wuhan Environmental Protection Bureau (武汉市环保局), Hubei Environmental Protection Agency (湖北省环境保护厅)) as well as the World Air Quality Index Project.
The World Air Quality Index project has exercised all reasonable skill and care in compiling the contents of this information and under no circumstances will the World Air Quality Index project team or its agents be liable in contract, tort or otherwise for any loss, injury or damage arising directly or indirectly from the supply of this data. All this historical Air Quality data is based on unvalidated, and due to quality assurance these data may be amended, without notice, at any time.
Data and information reported by the World Air Quality Index project are provided for the express purpose of providing citizens actionable health information related to air pollution. 

The following additional constraints apply to both direct and indirect data:

The data can not be sold or included in sold packages.
The data can not be used in paid applications or services.
The data can not be redistributed as cached or archived data.