move providers into providers subdirectory

providers/questrade/README.md

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+# Questrade Provider
+
+A provider for Questrade using the Questrade API.
+
+### Environment Variables
+
+* *questrade_account_[0...]* - A series of Questrade account numbers with a suffix of _0 and each additional account counting up.  
+* *questrade_ynab_account_[0...]* - The YNAB account ID for the matching questrade account.  Each configured questrade account must have a matching YNAB account.