[librsvg] New RELEASING.md with a release checklist

[Federico Mena Quintero <federico src gnome org>]

commit 2209620479c7e442dc025ae4419ee4ce5bd8760e
Author: Federico Mena Quintero <federico gnome org>
Date:   Wed Feb 24 18:33:02 2021 -0600

    New RELEASING.md with a release checklist

 RELEASING.md | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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+# Release process checklist for librsvg
+
+Feel free to print this document or copy it to a text editor to check
+off items while making a release.
+
+- [ ] Refresh your memory with https://wiki.gnome.org/MaintainersCorner/Releasing
+- [ ] Increase the package version number in `configure.ac` (it may already be increased but not released; 
double-check it).
+- [ ] Copy version number to `Cargo.toml`.
+- [ ] Tweak the library version number in `configure.ac` if the API changed; follow the steps there.
+- [ ] Update `NEWS`, see below for the preferred format.
+- [ ] Commit the changes above.
+- [ ] Make a tarball with `make distcheck DESTDIR=/tmp/foo` - fix things until it passes.
+- [ ] Create a signed tag - `git tag -s x.y.z` with the version number.
+- [ ] `git push` to the appropriate branch to gitlab.gnome.org/GNOME/librsvg
+- [ ] `git push` the signed tag to gitlab.gnome.org/GNOME/librsvg
+- [ ] `scp librsvg-x.y.z.tar.xz master.gnome.org:`
+- [ ] `ssh master.gnome.org` and then `ftpadmin install librsvg-x.y.z.tar.xz`
+- [ ] If this is a `x.y.0` release, [notify the release team][release-team] on whether to use it for the 
next GNOME version via an issue on their `GNOME/releng` project.
+
+## Version numbers
+
+`configure.ac` and `Cargo.toml` must have the same **package version**
+number - this is the number that users of the library see.
+
+`configure.ac` is where the **library version** is defined; this is
+what gets encoded in the SONAME of `librsvg.so`.
+
+Librsvg follows an even/odd numbering scheme for the **package
+version**.  For example, the 2.50.x series is for stable releases, and
+2.51.x is for unstable/development ones.  The [release-team] needs to
+be notified when a new series comes about, so they can adjust their
+tooling for the stable or development GNOME releases.  File an issue
+in their [repository][release-team] to indicate whether the new
+`librsvg-x.y.0` is a stable or development series.
+
+## Format for release notes in NEWS
+
+The `NEWS` file contains the release notes.  Please use something
+close to this format; it is not mandatory, but makes the formatting
+consistent, and is what tooling expects elsewhere.  Skim bits of the
+NEWS file for examples on style and content.
+
+New entries go at the **top** of the file.
+
+```
+=============
+Version x.y.z
+=============
+
+Commentary on the release; put anything here that you want to
+highlight.  Note changes in the build process, if any, or any other
+things that may trip up distributors.
+
+Next is a list of features added and issues fixed; use gitlab's issue
+numbers. I tend to use this order: first security bugs, then new
+features and user-visible changes, finally regular bugs.  The
+rationale is that if people stop reading early, at least they will
+have seen the most important stuff first.
+
+- #123 - title of the issue, or short summary if it warrants more
+  discussion than just the title.
+
+- #456 - fix blah blah (Contributor's Name).
+
+Special thanks for this release:
+
+- Any people that you want to highlight.  Feel free to omit this
+  section if the release is otherwise unremarkable.
+```
+
+## Making a tarball
+
+```
+make distcheck DESTDIR=/tmp/foo
+```
+
+The `DESTDIR` is a quirk, required because otherwise the gdk-pixbuf
+loader will try to install itself into the system's location for
+pixbuf loaders, and it won't work.  The `DESTDIR` is what Linux
+distribution packaging scripts use to `make install` the compiled
+artifacts to a temporary location before building a system package.
+
+## Copying the tarball to master.gnome.org
+
+If you don't have a maintainer account there, ask federico gnome org
+to do it or [ask the release team][release-team] to do it by filing an
+issue on their `GNOME/releng` project.
+
+[release-team]: https://gitlab.gnome.org/GNOME/releng/-/issues