Add README for C++ samples documenting setup, build, and usage

- Introduced a comprehensive README for C++ pdfRest API samples,
  covering prerequisites, installation, build, and execution
  instructions.
- Documented various sample categories: JSON payload, multipart payload,
  and complex workflows.
- Included environment variable setup, proxy support, and output
  handling details.
- Ensured clarity and consistency with existing sample documentation.

Author: datalogics-kam

CPlusPlus/README.md

@@ -0,0 +1,43 @@
+# C++ Samples for pdfRest
+
+These C++ examples mirror the DotNET samples: JSON Payload (upload → JSON call), Multipart Payload (single multipart request), and a Complex Flow (convert then merge). All binaries are placed in `build/` for convenience.
+
+## Prerequisites
+- CMake 3.16+ and a C++20 compiler (Clang/GCC/MSVC)
+- vcpkg (package manager): https://vcpkg.io/en/getting-started
+- pdfRest API key: https://pdfrest.com/getstarted/
+
+## Install Dependencies (vcpkg)
+- Install required libraries:
+  - `vcpkg install cpr nlohmann-json`
+- Tip: set `VCPKG_ROOT` to your vcpkg folder (e.g., `~/vcpkg`).
+  - Note: use the vcpkg CMake toolchain file; do not rely on `vcpkg integrate install`.
+
+## Build (macOS/Linux/Windows)
+- macOS/Linux:
+  - `cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=$VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake -DCMAKE_BUILD_TYPE=Release`
+  - `cmake --build build --parallel`
+- Windows (PowerShell):
+  - `cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE="$env:VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake" -DCMAKE_BUILD_TYPE=Release`
+  - `cmake --build build --config Release --parallel`
+  - Note: specifying `-DCMAKE_TOOLCHAIN_FILE=...` is required to use vcpkg with CMake across platforms.
+
+## Environment
+- Copy `.env.example` to `.env` and set:
+  - `PDFREST_API_KEY=your_api_key_here`
+  - Optional: `PDFREST_URL=https://eu-api.pdfrest.com` (EU/GDPR region). More info: https://pdfrest.com/pricing#how-do-eu-gdpr-api-calls-work
+
+## Run Samples
+- JSON two‑step (upload → JSON):
+  - `./build/markdown_json /path/to/input.pdf`
+  - `./build/rasterized_pdf_json /path/to/input.pdf`
+- Multipart (single POST):
+  - `./build/markdown_multipart /path/to/input.pdf`
+  - `./build/rasterized_pdf_multipart /path/to/input.pdf`
+- Complex flow (convert files to PDF, then merge):
+  - `./build/merge_different_file_types image.png slides.pptx`
+
+Notes
+- Output: responses are printed as JSON; non‑2xx results exit non‑zero with concise errors.
+- Proxies: respect `HTTPS_PROXY` / `HTTP_PROXY` if set.
+- Paths with spaces: quote your paths on all platforms.