Add readmE

README.md

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+# RedistributedDemurrageToken
+
+## Ownership
+
+* Contract creator is owner
+* Ownership can be transferred (also to ownership void contract)
+
+
+## Mint
+
+* Owner can add minters
+  - A faucet contract would be a minter
+* Minters can mint any amount
+
+
+## Demurrage
+
+* Decay amount (ppm) and period (blocks) is set at deploy time.
+  - Cannot be changed
+* Tax is applied when a **mint** or **transfer** is triggered for first time in new period;
+  - Supply _stays the same_.
+  - Updates `demurrageModiifer` which represents an exponential decay step.
+* All client-facing values (_balance output_ , _transfer inputs_) are adjusted with `demurrageModifier`.
+* Edge case: `approve` call, which may be called on either side of a period.
+
+
+## Redistribution
+
+* One redistribution entry is added to storage for each period;
+  - When `mint` is triggered, the new totalsupply is stored to the entry
+  - When `transfer` is triggered, and the account did not yet participate in the period, the entry's participant count is incremented.
+* Account must have "participated" in a period to be redistribution beneficiary.
+* Redistribution is applied when an account triggers a **transfer** for the first time in a new period;
+  - Check if have participated in period.
+  - Balance is increased by `(total supply at end of period * demurrage modifier ) / number of participants`
+  - Participation field is zeroed out.
+* Fractions must be rounded down (TODO)
+  - Remainder is "dust" and should be sent to a dedicated "sink" address (TODO)
+
+
+## Data structures
+
+* One word per account:
+  - bits 000-159: value
+  - bits 160-255: period
+  - (we have more room here in case we want to cram something else in)
+* One word per redistribution period:
+  - bits 000-055: period
+  - bits 056-215: supply
+  - bits 216-253: participant count
+  - bits     254: Set if invidiual redistribution amounts are fractions (TODO)
+  - bits     255: Set if "dust" has been transferred to sink (TODO)
+
+
+## QA
+
+* Basic python tests in place
+* How to determine and generate test vectors, and how to adapt them to scripts.
+* Audit sources?