Clarify WildFIRE-FM input channel contract

README.md

@@ -215,6 +215,9 @@ This Hub repository is model-first. It provides the released weights, model-load
 
 The pretrained checkpoints expect a fixed 16-channel tensor in `[channel, y, x]`
 order. Channel order matters.
+Inputs use native source units with no mean/std normalization, min/max scaling,
+or unit conversion. Invalid or missing values are zero-filled, with validity
+masks included as channels 10 and 11.
 
 | Channels | Names | Source |
 |---:|---|---|
@@ -228,6 +231,8 @@ used for supporting event-level tasks and are not part of the 16-channel
 pretrained occupancy input. Full channel-level details are in
 `data_sources/DATA_SOURCES.md`; the same contract is available as
 `models/wildfire_fm/input_channels.json`.
+The `cape` channel is the HRRR surface instantaneous CAPE field selected with
+`typeOfLevel=surface` and `stepType=instant`.
 
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