update the README for passing the det files when only DEM is passed without the circuit

Author: LalehB

README.md

@@ -43,8 +43,10 @@ We tested the Tesseract decoder for:
     suitable for large-scale simulations.
 *   **Efficient Beam Search:** implements a [beam search](https://en.wikipedia.org/wiki/Beam_search)
     algorithm to minimize decoding cost and enhance efficiency.
-*   **Sampling and Shot Range Processing:** supports sampling shots from circuits and processing
-    specific ranges of shots for flexible experiment setups.
+**Sampling and Shot Range Processing:** supports sampling shots from circuits. When a detection
+    error model is provided without an accompanying circuit, Tesseract requires detection events from
+    files using `--in`. The decoder can also process specific shot ranges for flexible experiment
+    setups.
 *   **Detailed Statistics:** provides comprehensive statistics output, including shot counts, error
     counts, and processing times.
 *   **Heuristics**: includes flexible heuristic options: `--beam`, `--det-penalty`,
@@ -94,6 +96,10 @@ Basic Usage:
 ./tesseract --circuit CIRCUIT_FILE.stim --sample-num-shots N --print-stats
 ```
 
+To decode pre-generated detection events, provide the input file using
+`--in SHOTS_FILE --in-format FORMAT`.
+
+
 Example with Advanced Options:
 
 ```bash