[gnome] Add clipboard manager extension

gnome/.local/share/gnome-shell/extensions/clipboard-history@alexsaveau.dev/README.md

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+# Gnome Clipboard History
+
+[Gnome Clipboard History](https://extensions.gnome.org/extension/4839/clipboard-history/) is a
+clipboard manager GNOME extension that saves what you've copied into an easily accessible,
+searchable history panel.
+
+The extension is a rewrite of
+[Clipboard Indicator](https://github.com/Tudmotu/gnome-shell-extension-clipboard-indicator) with
+vastly improved performance, new features, and
+[bug fixes](https://github.com/Tudmotu/gnome-shell-extension-clipboard-indicator/pull/338).
+
+A technical overview is available at https://alexsaveau.dev/blog/gch.
+
+## Project status: replaced by Ringboard
+
+Gnome Clipboard History is now in maintenance mode as it is being replaced by
+[Ringboard](https://github.com/SUPERCILEX/clipboard-history). I'm still accepting PRs for small
+improvements and bug fixes (such as supporting the latest Gnome version), but no new development
+will take place.
+
+## Download
+
+[<img src="https://raw.githubusercontent.com/andyholmes/gnome-shell-extensions-badge/eb9af9a1c6f04eb060cb01de6aeb5c84232cd8c0/get-it-on-ego.svg?sanitize=true" alt="Get it on GNOME Extensions" height="100" align="middle">](https://extensions.gnome.org/extension/4839/clipboard-history/)
+
+## Tips
+
+![Tutorial screenshot](tutorial-screenshot.png)
+
+- Open the panel from anywhere with <kbd>Super</kbd> + <kbd>Shift</kbd> + <kbd>V</kbd>.
+- Modify shortcuts in settings or delete them by hitting backspace while editing a shortcut.
+- Use the `Only save favorites to disk` feature to wipe your non-favorited items on shutdown.
+- Use `Private mode` to temporarily stop processing copied items.
+- Use keyboard shortcuts while the panel is open:
+  - <kbd>Ctrl</kbd> + <kbd>N</kbd> where `N` is a number from 1 to 9 to select the Nth
+    non-favorited entry.
+  - <kbd>Super</kbd> + <kbd>Ctrl</kbd> + <kbd>N</kbd> where `N` is a number from 1 to 9 to select
+    the Nth favorited entry.
+  - <kbd>Ctrl</kbd> + <kbd>p/n</kbd> to navigate to the previous/next page.
+  - <kbd>Ctrl</kbd> + <kbd>Alt</kbd> + <kbd>S</kbd> to open settings.
+  - <kbd>/</kbd> to search.
+  - <kbd>F</kbd> to (un)favorite a highlighted item.
+- Search uses case-insensitive [regex](https://regex101.com/?flavor=javascript).
+
+## Install from source
+
+A note on versioning:
+
+- The `master` branch and `1.4.x` tags support GNOME 45.
+- The `pre-45` branch and `1.3.x` (or earlier) tags support GNOME 40-44.
+
+### Build
+
+```shell
+cd ~/.local/share/gnome-shell/extensions/ && \
+  git clone https://github.com/SUPERCILEX/gnome-clipboard-history.git clipboard-history@alexsaveau.dev && \
+  cd clipboard-history@alexsaveau.dev && \
+  make
+```
+
+### Restart GNOME
+
+<kbd>Alt</kbd> + <kbd>F2</kbd> then type `r`.
+
+### Install
+
+```shell
+gnome-extensions enable clipboard-history@alexsaveau.dev
+```