create Readme Quickstart

Author: poma12390

examples/Linq2db.QuickStart/README.md

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+# Linq2DB YDB Quick Start
+
+A tiny sample that shows how to connect to **YDB** with **Linq2DB**, create tables, seed demo data, run parameterized queries and a transaction.
+
+## Running QuickStart
+
+1. **Start YDB Local**  
+   Follow the official guide: https://ydb.tech/docs/en/reference/docker/start  
+   Defaults expected by the sample:
+   - non‑TLS port: **2136**
+   - TLS port: **2135**
+   - database: **/local**
+
+2. **(Optional) Configure environment variables**  
+   The app reads connection settings from env vars (safe defaults are used if missing).
+
+   **Bash**
+   ```bash
+   export YDB_HOST=localhost
+   export YDB_PORT=2136
+   export YDB_DB=/local
+   export YDB_USE_TLS=false
+   # export YDB_TLS_PORT=2135
+   ```
+
+   **PowerShell**
+   ```powershell
+   $env:YDB_HOST="localhost"
+   $env:YDB_PORT="2136"
+   $env:YDB_DB="/local"
+   $env:YDB_USE_TLS="false"
+   # $env:YDB_TLS_PORT="2135"
+   ```
+
+3. **Restore & run**
+   ```bash
+   dotnet restore
+   dotnet run
+   ```