Add comprehensive step-by-step Phyphox recording guide

src/phyphox_app_block.py

@@ -64,15 +64,41 @@ def render_phyphox_tab(
     norm_params_path: str,
 ) -> None:
     st.subheader("Upload Phyphox sensor recording")
-    st.markdown("""
-**How to record your own data:**
-1. Install [Phyphox](https://phyphox.org/) on your phone
-2. Open **Acceleration (with g)** and **Gyroscope**: record simultaneously
-3. Hold the phone at your waist (same position as the UCI dataset)
-4. **Before recording:** tap the trash icon in Phyphox to clear any previous data
-5. Record 10–15 seconds of a single activity without pausing
-6. Export both experiments as CSV and upload below
-    """)
+    with st.expander("How to record and export your data — step by step", expanded=True):
+        st.markdown("""
+**Step 1 — Install Phyphox**
+Download the free [Phyphox](https://phyphox.org/) app from the Play Store (Android) or App Store (iOS).
+
+**Step 2 — Create a new experiment**
+- Open the app and tap the **+** icon in the top-right corner
+- Select **Add simple experiment**
+- In the active sensors list, add **Accelerometer** and **Gyroscope**
+- Set the **sensor rate to 50** (Hz) for both
+- Give the experiment a title (e.g. "Walking") then tap **Proceed**
+
+**Step 3 — Configure a timed run**
+- Tap the **⋮ (three-dot menu)** in the top-right corner and select **Timed run**
+- Set a **recording duration** (15–20 seconds recommended)
+- Optionally set a **start delay** (e.g. 5 seconds) so you have time to get into position before recording begins
+
+**Step 4 — Position the device**
+Place your phone in your **trouser pocket** or attach it at your **waist**. This mirrors how the original UCI dataset was collected and gives the most accurate results.
+
+**Step 5 — Record one activity**
+- Press the **play button** to start
+- Perform a **single activity continuously** — do not stop and restart mid-recording
+- Stay in steady motion for the full duration before stopping
+
+**Step 6 — Export the data**
+- After the recording ends, tap the **⋮ (three-dot menu)** and select **Export data**
+- Choose **CSV (comma separated values)** and confirm
+- You will receive a **.zip file** — unzip it to find separate CSV files for the **Accelerometer** and **Gyroscope**
+
+**Step 7 — Upload below**
+Upload each CSV file into its corresponding field below, then the pipeline will extract features and classify your activity.
+
+> ⚠️ **Important:** Each export is a fresh experiment. Do not reuse an old experiment — it will contain data from previous recordings stitched together, which will confuse the classifier.
+        """)
 
     if "phyphox_run" not in st.session_state:
         st.session_state.phyphox_run = 0