feat(docs/api/scripts): adding a How To run the refunds transaction o…

…n heroku

docs/api/scripts/refund-transactions.md

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+# Script
+
+The script opencollective-api [refund script](https://github.com/opencollective/opencollective-api/blob/master/scripts/add_refund_transactions_from_collective.js) tries to find transactions to refund given a **List/Array** of **FromCollectiveId** . 
+
+It looks through all transactions in the opencollective database and returns the transactions(that were still not refunded yet) that match the field **FromCollectiveId** with the Input List(as said above).
+
+## Running the Script
+
+### Set the HEROKU Environment variable
+
+You can log into heroku and go to the main dashboard(link: https://dashboard.heroku.com/apps/opencollective-prod-api)
+You'll see something like this
+
+
+### Go to the setting tabs
+
+Through the picture above you'll see multiple tabs, then look for the setting ones and click on the button `Reveal config vars`.
+
+You'll see a list with some variables and its respective values beside.
+
+
+### Edit the Environment Variable FROM_COLLECTIVE_IDS
+
+You look for the variable named `FROM_COLLECTIVE_IDS` and change it to the value you want. In case you don't find it on the list you can just add it.
+
+Example: 
+
+- if you want to refund all transactions that a collective with id X has done you'll set this `FROM_COLLECTIVE_IDS` to `X`:
+    - `FROM_COLLECTIVE_IDS`: X
+
+- if you want to refund all transactions that a collective with id X **AND** another collective with id Y has done you'll set this `FROM_COLLECTIVE_IDS` to `X,Y`:
+    - `FROM_COLLECTIVE_IDS`: X,Y    
+
+- if you want to refund all transactions that a collective with id X **AND** another collective with id Y **AND** another collective with id W has done you'll set this `FROM_COLLECTIVE_IDS` to `X,Y,W`:
+    - `FROM_COLLECTIVE_IDS`: X,Y,W
+
+- And so On...
+
+### Running heroku 
+
+We have more than one option here(using the heroku interface or using the terminal). I'll go with the terminal version:
+
+1. Make sure you have heroku installed in your machine
+2. Make sure you are logged in to the opencollective heroku account
+3. run in staging: `heroku run npm run refund-transactions --app opencollective-staging-api`
+4. run in production: `heroku run npm run refund-transactions --app opencollective-prod-api`