Upstream README

Author: BryceBeagle

README.md

@@ -6,3 +6,31 @@ This repository holds the stubs of the PyQt5 framework. It uses the stub files t
 produced during compilation process of PyQt5. These stub files have been modified by the author
 to allow using them for type-checking via Mypy. This repository is far from complete and the author will
 appreciate any PRs or Issues that help making this stub-repository more reliable.
+
+
+# Building upstream stubs
+The Dockerfile in the root of the `upstream` branch is used to build all* of the
+stubs for the upstream PyQt5 modules. The Dockerfile consists of multiple build
+layers:
+* core `PyQt5`
+* `PyQt3D`
+* `PyQtChart`
+* `PyQtDataVisualization`
+* `PyQtPurchasing`
+* `PyQtWebEngine`
+* an output layer. 
+
+Each module build layer deposits its stub files within `/output/` in its
+filesystem. The output layer then collects the contents of each into its own 
+`/output/` dir for export to the host computer. Build args are provided to 
+change the version of each module.
+
+A convenience script, `build_upstream.py`, is provided. It builds the stubs and 
+copies them to the host computer. Make sure you install `docker-py` to use it.
+It builds `$PWD/Dockerfile` (overridden with `--dockerfile`) and outputs the
+stubs to `$PWD/PyQt5-stubs` (overridden with `--output-dir`). 
+
+\* There are a few missing modules: `QtAxContainer`, `QtAndroidExtras`, 
+`QtMacExtras`, and `QtWindowsExtras`. The current project understanding is that
+they need to be built on the target platform, something a Linux-based docker
+image cannot do. The deprecated `Enginio` module is also missing.