Price data update (#82)

* Update price data

* Update price source in docs

Author: LadyChristina

docs/contribute.md

@@ -50,16 +50,19 @@ page](https://blockchain-technology-lab.github.io/tokenomics-decentralization/se
 ### Price information
 
 The directory `price_data/` contains information about the supported ledgers'
-market price. Each file in this folder is named `<project_name>.csv` (for the
+market price. Each file in this folder is named `<ledger>-USD.csv` (for the
 corresponding ledger). The csv file has no header and each line contains two
 comma-separated values:
 (i) a day (in the form YYYY-MM-DD);
-(ii) the USD market price of the token on the set day.
+(ii) the USD market price of the token on the set day (specifically its opening price).
+
+All price information is currently obtained from CoinGecko.
 
 To contribute price information you can either update an existing file, by
 adding entries for days where data is missing, or create a new file for a
 newly-supported ledger and add historical price data.
 
+
 ## Add metrics
 
 To add a new metric, you should do the following steps.

docs/data.md

@@ -197,6 +197,5 @@ There are also three command line arguments that can be used to customize the da
 
 ## Historical prices
 
-The historical market prices (available in `price_data`) were collected from
-[CoinMarketCap](https://coinmarketcap.com/) and
-[Statista](https://www.statista.com/).
+The historical market prices for all coins (available under `price_data`) were collected from
+[CoinGecko](https://www.coingecko.com/).