[mobile] Replace hardcoded provider url with env var (#4476)

* Replace hardcoded provider url with env var

* Update doc

mobile/README.md

@@ -62,6 +62,9 @@ To run the mobile app on your phone, you need to both start the Metro builder se
 
 If you want to use a physical device in combination with the marketplace DApp running on your local machine (i.e. `Localhost` setting in network selection) make sure you set the `HOST` environment variable to your internal network IP address (e.g. 10.10.10.1).
 
+### Build
+Make sure to set the env var MAINNET_PROVIDER_URL and RINKEBY_PROVIDER_URL. They are used [here](./src/constant.js)
+
 ### Tips
 
 > Is there a way to remotely debug the app?

mobile/src/constants.js

@@ -37,15 +37,13 @@ export const NETWORKS = [
     id: 1,
     name: 'Mainnet',
     dappUrl: 'https://shoporigin.com/#/',
-    provider:
-      'https://eth-mainnet.alchemyapi.io/v2/snPxmbyVLjq1Sq32Z4pAal7FXwe941uf'
+    provider: process.env.MAINNET_PROVIDER_URL
   },
   {
     id: 4,
     name: 'Rinkeby',
     dappUrl: 'https://dapp.staging.originprotocol.com/#/',
-    provider:
-      'https://eth-rinkeby.alchemyapi.io/v2/D0SsolVDcXCw6K6j2LWqcpW49QIukUkI'
+    provider: process.env.RINKEBY_PROVIDER_URL
   },
   {
     id: 2222,