Backfill Frob log events

pkg/transformers/shared/TransformerREADME.md

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+# Transformers
+
+## Description
+Transformers must be defined in order to define what events should trigger data updates and how those are performed.
+
+## Interface
+
+### Initializer
+Accepts DB and Blockchain from Vulcanize and returns a new transformer. E.g. for a new object "Cup":
+`func NewCupTransformer(db *postgres.DB, blockchain core.ContractDataFetcher) transformers.Transformer`
+
+### Execute
+Triggers operations to take in response to a given log event.
+Can persist data from logs, fetch and persist arbitrary data from outside services (e.g. contract state), or take any number of other actions. E.g.:
+`func (cupTransformer *CupTransformer) Execute() error`
+
+## Additional Requirements
+Transformers must define log filters and create them so that relevant watched events can be identified and retrieved. E.g.:
+```$xslt
+	{
+		Name:      "CupsBite",
+		FromBlock: 0,
+		ToBlock:   -1,
+		Address:   "0x448a5065aebb8e423f0896e6c5d525c040f59af3",
+		Topics:    core.Topics{"0x40cc885400000000000000000000000000000000000000000000000000000000"},
+	},
+```