Add README

README.md

 # plutus-payment-sheets
+
+`plutus-payment-sheets` is a CSV/spreadsheet toolkit for use with plutus smart
+contracts. This uses
+[composite-base](https://hackage.haskell.org/package/composite-base) and
+[sheets](https://gitlab.homotopic.tech/haskell/sheets) to provide extensible
+records with JSON instances so that row data can be submitted to PAB in a
+compatible way. This also uses
+[plutus-cassava](https://gitlab.homotopic.tech/plutus/libs/plutus-cassava) for
+cassava instances for common plutus types such as CurrencySymbol and PaymentPubKeyHash.
+
+This library also comes with some default conventions to use for columns for
+standard operations.
+
+To make your own sheets, decide what fields you want in the sheet.
+
+```{.haskell}
+import qualified Composite.Csv as Csv
+import Composite.Record
+import Composite.Sheet
+import Composite.TH
+
+withLensesAndProxies [d|
+
+   type FRecipient = "recipient" :-> PaymentPubKeyHash
+
+   type FTokenName = "tokenName" :-> TokenName
+
+   type FAmountToMint = "amountToMint" :-> Integer
+
+   |]
+
+type MintOrderIxs = '[FRecipient, FTokenName, FAmountToMint]
+
+type MintOrder = Sheet [] MintOrderIxs
+```
+
+Derive some instances.
+
+```{.haskell}
+deriving newtype instance FromField FRecipient
+
+deriving newtype instance FromField FTokenName
+
+deriving newtype instance FromField FAmountToMint
+
+deriving newtype instance ToField FRecipient
+
+deriving newtype instance ToField FTokenName
+
+deriving newtype instance ToField FAmountToMint
+
+deriving via (Csv.TF Identity MintOrderIxs) instance FromNamedRecord (Record MintOrderIxs)
+
+deriving via (Csv.TF Identity MintOrderIxs) instance ToNamedRecord (Record MintOrderIxs)
+```
+
+That's it. Now you can make a csv of the form.
+
+```
+recipient, tokenName, amountToMint
+adsdfsdf, fdf, 1
+bdfsdsd, zzzz, 1
+```
+
+Using a PAB endpoint with type `MintOrder`. For a complete example of how to
+use this, see the
+[plutus-contract-osc](https://gitlab.homotopic.tech/plutus/contracts/osc)
+contract example that accepts mint orders of this type.