doc: write out the fee recommendation

doc/fee-recommendation.md

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+Dogecoin Fee Recommendation
+----------------------------
+
+_last updated for 1.14.5_
+
+The Dogecoin chain has a relatively low block interval, 1 megabyte blockspace
+and aims to provide a cheap means for people to transact. Therefore, the biggest
+threat to the Dogecoin chain as a whole is spam and in 2014, a transaction fee
+and dust disincentive were introduced, to combat on-chain spam.
+
+Dogecoin Core implements a number of defaults into the software that reflect the
+developers' recommendations towards fees and dust limits, that at the moment of
+release represent the developers best estimate of how these limits should be
+parametrized. The recommended defaults, as implemented in the Dogecoin Core
+wallet, are:
+
+- **0.01 DOGE per kilobyte** transaction fee
+- **1.00 DOGE** dust limit (discard threshold)
+- **0.001 DOGE** replace-by-fee increments
+
+The wallet rejects transactions that have outputs under the dust limit, and
+discards change to fee if it falls under this limit.
+
+Note: The recommended dust limit is expected to be lowered in a follow-up
+      release, once enough miners and relay nodes have adopted newly introduced
+      relay dust limits touched upon below.
+
+Note: In the past, Dogecoin has enforced a rounding function in the fee
+      mechanism. As of version 1.14.5, this is no longer the case, and fees are
+      calculated over the exact size of a transaction. For example, a 192 byte
+      transaction only has to pay `0.01 / 1000 * 192 = 0.00192` DOGE fee.
+
+## Miner default inclusion policies
+
+The default values for miners to include a transaction in a block has been set
+to exactly the recommended fee of **0.01 DOGE/kB.** Dust limits are defined by
+the miner's mempool policy, see below.
+
+## Relay and mempool policies
+
+The relay and mempool acceptance policies are lower than the recommendations
+by default, to allow for a margin to change recommendations in the future (or
+user preference) without the need for an adopted software release in advance.
+This greatly simplifies future policy recommendations. As historically, most
+relay nodes do not change these default settings, these often represent an
+absolute mininum
+
+### Transaction fee
+
+The default minimum transaction fee for relay is set at **0.001 DOGE/kB**,
+exactly one-tenth of the recommended fee. This gives miners and relay operators
+a 10x downward margin to operate within from a spam management perspective.
+
+### Dust limits
+
+The mempool logic implements 2 dust limits, a hard dust limit under which a
+transactions is considered non-standard and rejected, and a soft dust limit
+that requires the limit itself to be added to the transaction fee, making the
+output economically unviable.
+
+- The hard dust limit is set at **0.001 DOGE** - outputs under this value are
+  invalid and rejected.
+- The soft dust limit is set at **0.01 DOGE** - sending a transaction with outputs
+  under this value, are required to add 0.01 DOGE for each such output, or else
+  will be considered to have too low fee and be rejected.
+
+### Replace-by-fee and mempool limiting increments
+
+The increments used for replace-by-fee and limiting the mempool once it has
+reached its locally defined maximum size, is by default set at one-tenth of
+the relay fee, or **0.0001 DOGE**.