add Trezor setup cheat-sheet

docs/common-tasks/setup-trezor-cryptocurrency-hardware-wallet.md

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+## Setting up a Trezor cryptocurrency hardware wallet in Qubes
+
+using a Fedora-based sys-usb VM and a Whonix WS-based application VM:
+
+- in dom0:
+    `sudo vim /etc/qubes-rpc/policy/trezord-service`
+add this line:
+        `$anyvm $anyvm allow,user=trezord,target=sys-usb`
+replace `sys-usb` with `disp-sys-usb` if you are using a disposable sys-usb
+
+- in the sys-usb VM, or for disp-sys-usb, the VM on which it is based
+  (in both cases, assumed to use a fedora-3x template):
+	`sudo mkdir /usr/local/etc/qubes-rpc`
+	`sudo vim /usr/local/etc/qubes-rpc/trezord-service`
+	and add this line to trezord-service:
+	`socat - TCP:localhost:21325`
+- in the whonix-based application VM:
+    `pip3 install --user trezor`
+    `sudo vim /rw/config/rc.local`
+	add this line (note the "&" at the end):
+    `socat TCP-LISTEN:21325,fork EXEC:"qrexec-client-vm sys-usb trezord-service" &`
+
+- in the fedora-3x template:
+    `sudo dnf install trezor-common`
+
+- download the bridge RPM from
+    https://wallet.trezor.io/#/bridge
+	and remember to verify it!
+- copy to fedora-3x
+- in fedora-3x
+    `sudo rpm -i /path/to/trezor.rpm`