docs: add clear installation guide for Windows and Raspberry Pi

[Hongwei-Z]

Motivation

While working with liboqs-python, I noticed that setting up the underlying C library (liboqs) on Windows can be quite challenging for newcomers. The current documentation leaves some room for ambiguity, and following it often leads to environment configuration issues and build errors.

After multiple rounds of trial and error, I have summarized a highly concise, beginner-friendly guide that ensures a smooth and straightforward installation on Windows.

Furthermore, as Post-Quantum Cryptography (PQC) research increasingly intersects with IoT and edge computing, many researchers need to deploy these libraries on resource-constrained hardware. To support the research community, I have also contributed an installation guide for Raspberry Pi (ARM) devices.

Key Changes

• INSTALL-Windows.md: A streamlined, step-by-step guide to compiling the C library and setting up the Python wrapper on Windows, designed to bypass common pitfalls.
• INSTALL-RaspberryPi.md: A hardware-specific guide tailored for researchers, detailing dependencies and build steps optimized for Raspberry Pi environments.
• README.md: Added direct index links to these new guides in the Installation section.

I hope these additions reduce the friction for new developers and researchers adopting this excellent library. Let me know if any adjustments are needed!

[dstebila]

Thanks for the contribution, @Hongwei-Z. I am thinking it might be better to fold a shortened version of this into the main README, both so that it's more prominent, and so that it doesn't need to repeat material present in the main README.

What do you think about adding the following as a subsections of "Installation -- Configure, build, and install liboqs"?

---

Platform-specific notes

The instructions above apply to all platforms; the notes below cover
prerequisites that are easy to miss on Windows and on Debian-based Linux
(including Raspberry Pi).

Windows. If you do not already have a C++ compiler and CMake, install the
Build Tools for Visual Studio
(scroll to "All Downloads" → "Tools for Visual Studio"). In the installer,
select the Desktop development with C++ workload, which provides the MSVC
compiler, the Windows SDK, and CMake. Then run the CMake commands from a
Developer Command Prompt for VS so the compiler is on your PATH. Remember
the -DCMAKE_WINDOWS_EXPORT_ALL_SYMBOLS=TRUE flag and the PATH setting for
oqs.dll described above.

Debian-based Linux (including Raspberry Pi). Install the build
prerequisites with

sudo apt update
sudo apt install -y build-essential cmake ninja-build libssl-dev git python3-pip python3-venv

After cmake --build ... --target install, run sudo ldconfig so the newly
installed shared library is found at runtime (an alternative to setting
LD_LIBRARY_PATH as described above).

[Hongwei-Z]

Thanks for the review and the suggestion @dstebila! I like this approach. Consolidating the platform-specific notes into the main README will make them more visible and avoid maintaining duplicate documentation.
I'll revise this PR accordingly by replacing the separate document with a concise Platform-specific notes subsection under Installation → Configure, build, and install liboqs. Please let me know if you'd like any further adjustments.

[Hongwei-Z]

I've updated the PR based on your suggestion. The platform-specific notes have been integrated into the main README under the installation section, and the separate document has been removed to avoid duplication. Thanks again for the helpful suggestion!