Rewrite README install section as a 6-step walkthrough

Replace the terse install summary with a click-by-click guide that
covers the full setup in both README.md and README.zh-CN.md:
clone+pip, GCP service account, moving the key out of the repo,
creating the sheet with header row, writing config.json, and a
sanity check. Flag the zh-CN tab-name gotcha (工作表1 vs Sheet1)
that causes HTTP 400 Unable to parse range.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -16,18 +16,78 @@ Intended to be invoked manually inside Claude Code today, and wired up to a What
 
 ## Install
 
-Clone into your Claude Code skills directory:
+Follow the 6 steps below. Takes ~10 minutes.
+
+### Step 1 — Clone the skill and install Python deps
 
 ```bash
 git clone https://git.deepknow.site/Knowit/AutoACCT.git ~/.claude/skills/bookkeeping
+pip install google-api-python-client google-auth
 ```
 
-Then follow [`scripts/setup.md`](scripts/setup.md) for the one-time setup:
+### Step 2 — Create a Google Cloud service account
 
-- Python deps: `pip install google-api-python-client google-auth`
-- Create a GCP service account + download its JSON key
-- Create a Google Sheet, add 14 header columns, share with the service account email
-- `cp config.example.json config.json` and fill in `sheet_id` + `service_account_path`
+1. Open https://console.cloud.google.com/ and create a new project (e.g. `autoacct`).
+2. In the top search bar, search **Google Sheets API** → click the result → **Enable**.
+3. Left menu: **IAM & Admin → Service Accounts → + Create Service Account**
+   - Name: `bookkeeping` (any name works)
+   - Click **Create and Continue → Done** (skip the optional role step).
+4. Click the new service account → **Keys** tab → **Add Key → Create new key → JSON → Create**.
+   A `.json` key file will download to your browser's Downloads folder.
+5. **Copy the service account's email** (looks like `bookkeeping@<project>.iam.gserviceaccount.com`) — you'll paste it in Step 4.
+
+### Step 3 — Move the key file out of the repo
+
+Never leave a service-account key inside the repo directory. Move it to `~/.config/gcp/`:
+
+```bash
+mkdir -p ~/.config/gcp
+mv ~/Downloads/<your-downloaded-file>.json ~/.config/gcp/bookkeeping-sa.json
+chmod 600 ~/.config/gcp/bookkeeping-sa.json
+```
+
+### Step 4 — Create the Google Sheet
+
+1. Open https://sheets.new (creates a fresh blank sheet).
+2. Give it a title (e.g. `AutoACCT Expenses`).
+3. **Note the tab name** at the bottom-left — default is `Sheet1` (English UI) or `工作表1` (Chinese UI). Write it down, you'll need the exact string in Step 5.
+4. Click cell **A1**, then paste this one line (the tabs split the headers across A–N automatically):
+   ```
+   Date	Merchant	Category	Amount	Currency	Amount (HKD)	FX Rate	FX Date	Payment Method	Line Items	Raw OCR	Note	Receipt	Logged At
+   ```
+5. Click **Share** (top right) → paste the service-account email from Step 2 → role **Editor** → **Send** (you can uncheck "Notify people").
+6. Copy the **Sheet ID** from the URL — it's the long string between `/d/` and `/edit`:
+   `https://docs.google.com/spreadsheets/d/`**`1abc...xyz`**`/edit`
+
+### Step 5 — Write config.json
+
+```bash
+cd ~/.claude/skills/bookkeeping
+cp config.example.json config.json
+```
+
+Open `config.json` in your editor and fill in **sheet_id** and **worksheet** with the values from Step 4:
+
+```json
+{
+  "sheet_id": "1abc...xyz",
+  "worksheet": "Sheet1",
+  "service_account_path": "~/.config/gcp/bookkeeping-sa.json",
+  "hkd_fx_provider": "frankfurter"
+}
+```
+
+> ⚠️ **Common pitfall**: if your Google Sheets UI is in Chinese, the default tab is named `工作表1` (not `Sheet1`). Put `"worksheet": "工作表1"` exactly. A mismatched tab name throws `HTTP 400: Unable to parse range`.
+
+### Step 6 — Sanity check
+
+```bash
+echo '{"date":"2026-04-20","merchant":"TEST","category":"Other","amount":1,"currency":"HKD","amount_hkd":1,"fx_rate":1,"fx_date":"2026-04-20"}' | python3 ~/.claude/skills/bookkeeping/scripts/append_row.py
+```
+
+Success looks like: `OK 'Sheet1'!A2:N2` and a new row appears in the sheet. Delete the TEST row when you're done.
+
+If you hit an error, see [`scripts/setup.md`](scripts/setup.md) for the longer reference.
 
 ## Use