docs: add build guide and CI.

README.md

@@ -15,13 +15,6 @@ The original author compiled following binaries:
 - [0.1.0 alpha](https://github.com/olive-editor/olive/releases/tag/0.1.0)
 - [0.2.0 unstable development build](https://github.com/olive-editor/olive/releases/tag/0.2.0-nightly)
 
-## OpenFX Support TODO
-- Implement plugin discovery/loading from a given path and populate the cache (currently creates host/cache only). `app/pluginSupport/OliveHost.cpp`
-- Wire output clip image storage: allocate a backing buffer, set `kOfxImagePropData`, and update bounds/rowBytes before render. `app/pluginSupport/OliveClip.cpp`
-- Provide real input clip image fetches (currently returns an empty `Image` for inputs). `app/pluginSupport/OliveClip.cpp`
-- Ensure render path sets per-frame output data and handles ROD/bounds correctly. `app/render/plugin/pluginrenderer.cpp`
-- Add missing param instance types (String, Double3D/Integer3D, Group/Page, Custom/Bytes) and mapping to node inputs. `app/pluginSupport/OlivePluginInstance.cpp`, `app/node/plugins/Plugin.cpp`
-- Implement `editBegin`/`editEnd`, progress, and timeline hooks instead of stubs. `app/pluginSupport/OlivePluginInstance.cpp`, `app/pluginSupport/OlivePluginInstance.h`
-- Integrate persistent message handling with the app UI (currently TODO placeholders). `app/pluginSupport/OlivePluginInstance.cpp`
-- Decide and enforce project extent/fielding behavior instead of the current placeholder comment. `app/pluginSupport/OlivePluginInstance.cpp`
-- Add OpenGL texture render suite support or explicitly disable it (currently `loadTexture` returns null). `app/pluginSupport/OliveClip.h`
+## Building from Source
+
+See [`docs/build.md`](docs/build.md) for build instructions on Windows (MSYS2), Linux (Debian/Ubuntu, Fedora, Arch Linux), and macOS.