[gnome-shell] extensions-tool: Add (back) README.md

[Florian Müllner <fmuellner src gnome org>]

commit 4e9154ca647978b3cef7552b2b87d3bb2e3b4591
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Dec 3 01:58:19 2019 +0100

    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

 subprojects/extensions-tool/README.md | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
---
diff --git a/subprojects/extensions-tool/README.md b/subprojects/extensions-tool/README.md
new file mode 100644
index 0000000000..1416abe1da
--- /dev/null
+++ b/subprojects/extensions-tool/README.md
@@ -0,0 +1,14 @@
+# 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