add MacOS and Windows installation steps

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## [0.3.1] (in development)
 
+* Added: Thanks to @lepapareil, @hurlenko and @ballsteve for contributing installation docs for Windows and MacOS.
+
 ## [0.3.0] 2021-27-05
 
 * Change `Parser::parse_file/string_with_encoding` to `Parser::parse_file/string_with_options`. 

README.md

@@ -17,3 +17,40 @@ As of the `0.2.0` release of the crate, there are some modest safety guarantees:
 **Coverage**: Only covers a subset of libxml2 at the moment, contributions are welcome. We try to increase support with each release.
 
 **Welcome!** With these caveats, the contributors to the project are migrating production work towards Rust and find a continuing reliance on libxml2 a helpful relief for initial ports. As such, contributions to this crate are welcome, if your workflow is not yet fully supported.
+
+## Installation prerequisites
+
+Before performing the usual cargo build/install steps, you need to have the relevant components for using the original libxml2 code. These may become gradually outdated with time - please do let us know by opening a new issue/PR whenever that's the case.
+
+### Linux/Debian
+
+On linux systems you'd need the development headers of libxml2 (e.g. `libxml2-dev` in Debian), as well as `pkg-config`.
+
+### MacOS
+[Community contributed](https://github.com/KWARC/rust-libxml/issues/88#issuecomment-890876895):
+
+```
+$ brew install libxml2 # e.g. version 2.9.12 
+$ ln -s /usr/local/Cellar/libxml2/2.9.12/lib/libxml2.2.dylib /usr/local/lib/libxml-2.0.dylib
+$ export LIBXML2=/usr/local/Cellar/libxml2/2.9.12/lib/pkgconfig/libxml-2.0.pc
+```
+
+### Windows
+
+[Community contributed](https://github.com/KWARC/rust-libxml/issues/81#issuecomment-760364976):
+
+* manually install builds tools c++ and english language by visiting [BuildTools](https://visualstudio.microsoft.com/fr/thank-you-downloading-visual-studio/?sku=BuildTools&rel=16)
+* manually install choco by visiting [its chocolatey page](https://docs.chocolatey.org/en-us/choco/setup)
+* launch cmd prompt with admin privileges and execute these commands sequentially:
+```
+C:\> choco install -y curl git unxUtils winlibs-llvm-free
+C:\> refreshenv
+C:\> %ChocolateyInstall%\bin\curl --output "c:\rustup-init.exe" "https://static.rust-lang.org/rustup/dist/i686-pc-windows-gnu/rustup-init.exe"
+C:\> c:\rustup-init.exe -y --default-toolchain stable-x86_64-pc-windows-msvc
+C:\> git clone https://github.com/microsoft/vcpkg
+C:\> .\vcpkg\bootstrap-vcpkg.bat
+C:\> setx /M PATH "%PATH%;c:\vcpkg" && setx VCPKGRS_DYNAMIC "1" /M
+C:\> refreshenv
+C:\> vcpkg install libxml2:x64-windows
+C:\> vcpkg integrate install
+```