Document a convention for encouraging donations

The convention smuggles an address in the node nickname and uses Zcash
shielded transactions for privacy.

docs/accepting-donations.rst

@@ -0,0 +1,78 @@
+========================
+Storage Server Donations
+========================
+
+The following is a configuration convention which allows users to anonymously support the operators of storage servers.
+Donations are made using `Zcash shielded transactions`_ to limit the amount of personal information incidentally conveyed.
+
+Sending Donations
+=================
+
+To support a storage server following this convention, you need several things:
+
+* a Zcash wallet capable of sending shielded transactions
+  (this *may* require a Zcash full node)
+* a shielded address with sufficient balance
+* a running Tahoe-LAFS client node which knows about the recipient storage server
+
+For additional protection, you may also wish to operate your Zcash wallet and full node using Tor.
+
+Find Zcash Shielded Address
+---------------------------
+
+To find an address at which a storage server operator wishes to receive donations,
+launch the Tahoe-LAFS web UI::
+
+  $ tahoe webopen
+
+Inspect the page for the storage server area.
+This will have a heading like *Connected to N of M known storage servers*.
+Each storage server in this section will have a nickname.
+A storage server with a nickname beginning with ``zcash:`` is signaling it accepts Zcash donations.
+Copy the full address following the ``zcash:`` prefix and save it for the next step.
+This is the donation address.
+Donation addresses beginning with ``z`` are shielded.
+It is recommended that all donations be sent from and to shielded addresses.
+
+Send the Donation
+-----------------
+
+First, select a donation amount.
+Next, use a Zcash wallet to send the selected amount to the donation address.
+Using the Zcash cli wallet, this can be done with a command like::
+
+  $ zcash-cli z_sendmany $YOUR_ADDRESS '[{"address": "$DONATION_ADDRESS", "amount": $AMOUNT}]'
+
+Remember that you must also have funds to pay the transaction fee
+(which defaults to 0.0001 ZEC in mid-2018).
+
+You can find ``$YOUR_ADDRESS`` using one of several commands.
+To find
+
+Receiving Donations
+===================
+
+To receive donations from users following this convention, you need the following:
+
+* a Zcash shielded address
+
+Configuring Tahoe-LAFS
+----------------------
+
+The Zcash shielded address is placed in the storage server's ``nickname`` field.
+Edit ``tahoe.cfg`` and edit the ``nickname`` field in the ``node`` section like so::
+
+  [node]
+  nickname = zcash:zABCDEF....
+
+Then restart the storage server.
+
+Further Reading
+===============
+
+To acquiant yourself with the security and privacy properties of Zcash,
+refer to the `Zcash documentation`_.
+
+.. _Zcash shielded transactions: https://z.cash/support/security/privacy-security-recommendations.html#transaction
+
+.. _Zcash documentation: https://z.cash/technology/index.html

docs/index.rst

@@ -32,6 +32,7 @@ Contents:
 
    backdoors
    donations
+   accepting-donations
    expenses
    cautions
    write_coordination