extensions-tool: Add (back) README.md

This was dropped when importing the project into gnome-shell. Now
that is a bit more separate again, it makes sense to add it back.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/877

diff --git a/subprojects/extensions-tool/README.md b/subprojects/extensions-tool/README.md
new file mode 100644 (file)
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--- /dev/null
+++ b/subprojects/extensions-tool/README.md
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+# gnome-extensions-tool
+gnome-extensions-tool is a command line utility for managing
+GNOME Shell extensions. It is usually built as part of gnome-shell,
+but can be used as a stand-alone project as well (for example to
+create an extension bundle as part of continuous integration).
+
+Bugs should be reported to the GNOME [bug tracking system][bug-tracker].
+
+## License
+gnome-extensions-tool is distributed under the terms of the GNU General Public
+License, version 3 or later. See the [COPYING][license] file for details.
+
+[bug-tracker]: https://gitlab.gnome.org/GNOME/gnome-shell/issues
+[license]: COPYING