lightweight sept dox

docs/components/fusee/sept.md

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+# sept
+Sept is a payload that facilitates booting Atmosphère when targeting firmware version 7.0.0+.
+
+It consists of a primary and a secondary payload.
+
+## Sept-Primary
+Sept-primary is essentially a stand-in for Nintendo's package1ldr, on 7.0.0+. To use it, the caller (normally Fusée-secondary) loads the sept-primary binary to `0x4003F000`,
+loads the 7.0.0+ TSEC firmware to `0x40010F00`, and loads a signed, encrypted payload to `0x40016FE0`.
+
+This signed, encrypted payload is normally Sept-secondary.
+
+## Sept-Secondary
+Sept-secondary is a payload that performs 7.0.0+ key derivation, and then chainloads to `sept/payload.bin`.
+
+It is normally stored encrypted/signed; if one wishes to build sept-secondary instead of using release builds, one must bring his/her own keys.