Add README for packagers

Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>

README-packaging.md

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+# Packaging Node.js
+These instructions are applicable as of 2023-04-27, following the
+implementation of https://www.fedoraproject.org/wiki/Changes/NodejsRepackaging
+
+
+## Basic steps to update to a new release
+
+1.  Run the following command to automatically update the specfile and SOURCES:
+
+    ```
+    ./nodejs-sources 20.1.0
+    ```
+
+    This will download the tarball from nodejs.org, strip out the bundled
+    OpenSSL code, extract the versions of the bundled sources, pull down the
+    ICU data files and update the spec file with this new information, also
+    pushing the rebuilt tarball into the Fedora lookaside cache.
+
+2.  Verify that the patches still apply by running `fedpkg prep`. If they do
+    not, follow the steps under "Resolving Patch Conflicts".
+
+3.  (Preferred) Perform a scratch-build on at least one architecture
+
+    ```
+    fedpkg scratch-build [--arch x86_64] --srpm
+    ```
+
+    Verify that it built successfully.
+
+4.  Commit the code locally and push it to all active Fedora branches.
+
+    ```
+    git commit -sam "Update to version 20.1.0"
+    ```
+
+    ```
+    git push origin rawhide rawhide:f38 rawhide:f37
+    ```
+
+5.  Build for all active Fedora branches
+
+    ```
+    for i in f37 f38 rawhide ; do fedpkg --release $i build --nowait ; done
+    ```
+
+
+## Basic steps to update the packaging
+
+1.  Make all changes in the `packaging/nodejs.spec.j2` file.
+
+2.  When finished, run
+
+    ```
+    ./nodejs-sources 20.1.0 --no-push
+    ```
+
+    which will regenerate the nodejs20.spec file with the appropriate values.
+    The `--no-push` argument is used to avoid uploading a new tarball to the
+    lookaside cache.[^1]
+
+3. (Preferred) Perform a scratch-build on at least one architecture
+
+    ```
+    fedpkg scratch-build [--arch x86_64] --srpm
+    ```
+
+    Verify that it built successfully.
+
+4.  Commit the code locally and push it to all active Fedora branches.
+
+    ```
+    git commit -sam "Update to version 20.1.0"
+    ```
+
+    ```
+    git push origin rawhide rawhide:f38 rawhide:f37
+    ```
+
+5.  Build for all active Fedora branches
+
+    ```
+    for i in f37 f38 rawhide ; do fedpkg --release $i build --nowait ; done
+    ```
+
+
+## Resolving Patch Conflicts
+
+1.  Clone the upstream Node.js repository
+
+    ```
+    git clone -o upstream git://github.com/nodejs/node.git nodejs-upstream
+    ```
+
+2. Rebase the Fedora patches atop the latest release
+
+    ```
+    pushd nodejs-upstream
+    ```
+
+    ```
+    git checkout -b fedora-v20 v20.1.0
+    ```
+
+    ```
+    git am -3 ../nodejs-fedora/*.patch
+    ```
+
+    If the patches do not apply cleanly, resolve the merges appropriately. Once
+    they have all been applied, output them again:
+
+    ```
+    git format-patch -M --patience --full-index -o ../nodejs20 v20.1.0..HEAD
+    ```
+
+    ```
+    popd
+    ```
+
+3.  Resume the basic process.
+
+
+[^1]: Due to non-deterministic behavior, stripping out the OpenSSL bits from
+    the upstream tarball and recompressing it will result in a different
+    checksum hash. This isn't harmful, but wastes bandwidth and storage space,
+    so use `--no-push` when possible.