Workaround for rngd cpu overload on rpi

Author: TitaniumHocker

src/installation/guides/arm-devices/platforms.md

@@ -45,6 +45,13 @@ In order to fix this, install the `rng-tools` package and
 [enable](../../../config/services/index.md#enabling-services) the `rngd`
 service, which uses the `/dev/hwrng` device to seed `/dev/random`.
 
+Sometimes `rngd` can cause CPU overload. To prevent this inefficient entropy
+sources must be excluded and HWRNG device forced:
+
+```
+echo "RNGD_OPTS='-x jitter -x pkcs11 -x rtlsdr -n hwrng'" > /etc/sv/rngd/conf
+```
+
 ### Graphical session
 
 The `mesa-dri` package contains drivers for all the Raspberry Pi variants, and