Add a quick README

Signed-off-by: Michał Górny <[email protected]>

Author: mgorny

README.rst

@@ -0,0 +1,86 @@
+====================================================
+Dockerfiles for building kernel/PyPy binary packages
+====================================================
+
+
+Configuration
+=============
+Before running any builds, you may want to create ``localconfig.bash``.
+This file is sourced automatically and contains environment variables
+to configure the builds.  The common use is to define
+``DOCKER_HOST_${ARCH}`` variables, to list hosts used for builds, e.g.::
+
+    DOCKER_HOST_ARM64=ssh://jiji.arm.dev.gentoo.org
+    DOCKER_HOST_PPC64LE=ssh://bogsucker.ppc64.dev.gentoo.org
+
+All builds require ``local.diff`` file which is applied on top of
+``gentoo.git``.  You prepare your changes, then do e.g.::
+
+    git diff origin > ${BINPKG_DOCKER}/local.diff
+
+This is done automatically by ``bump-kernels`` script
+from mgorny-dev-scripts_.
+
+
+Building kernels
+================
+The usual way to build kernels is to prepare the bumps and write them
+into ``local.diff``, e.g. using::
+
+    bump-kernel 6.6.{7,8} 6.1.{68,69} 5.15.{143,143} 5.10.{204,205}
+
+Then run the following target::
+
+    make ${ARCH}-gentoo-kernel-${VERSION}
+
+Where ``ARCH`` is one of: ``amd64``, ``arm64``, ``ppc64le``, ``x86``,
+and ``VERSION`` is two-component version, e.g.::
+
+    make amd64-gentoo-kernel-{6.{6,1},5.{15,10}}
+
+
+Building PyPy
+=============
+Bump the main and ``-exe`` PyPy builds, and write the changes
+to ``local.diff``, e.g.::
+
+    cd dev-python/pypy-exe
+    pkgbump pypy-exe-7.3.{13,14}.ebuild
+    pkgcommit --bump
+    cd ../pypy
+    pkgbump pypy-7.3.{13,14}.ebuild
+    pkgcommit --bump
+    git diff origin > ${BINPKG_DOCKER}/local.diff
+
+Afterwards run the target::
+
+    make ${ARCH}-pypy${SUFFIX}
+    make ${ARCH}-musl-pypy${SUFFIX}
+
+No suffix means building PyPy2.7, otherwise a suffix such as ``3_9``
+or ``3_10`` is to be used (matching package name).
+
+
+Transferring binary packages
+============================
+The ``rsync`` target is provided to copy ``~/binpkg`` tree from all
+Docker hosts to the current machine, and then to your devspace::
+
+    make rsync
+
+
+Build dependency cache
+======================
+When building dependencies, the process automatically keeps a cache
+of binary package within the image.  For this cache to be useful,
+it needs to be copied to the host by running::
+
+    make ${ARCH}-kernel-sync
+
+Then, when running builds one needs to start a web server with
+the packages::
+
+    python -m http.server -b 127.0.0.1 -d binpkg-cache/amd64 8787
+
+
+.. _mgorny-dev-scripts: https://github.com/projg2/mgorny-dev-scripts/