Automate the installation asciinema screencast

docs/misc/asciinema/Dockerfile

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+FROM fedora:35
+RUN dnf install -y wget
+RUN dnf install -y expect
+COPY ./install.tcl ./run-install.sh /asciinema/

docs/misc/asciinema/README.rst

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+Do NOT run the examples without isolation (e.g docker) or 
+this code may make undesirable changes to your host.
+
+To this:
+```sh
+docker build --tag borg-examples .
+asciinema rec -c 'docker run --rm borg-examples bash /asciinema/run-install.sh' --overwrite ./install.json
+```

docs/misc/asciinema/install.tcl

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+# Configuration for send -h
+# Tries to emulate a human typing
+# Tweak this if typing is too fast or too slow
+set send_human {.05 .1 1 .01 .2}
+
+set script [string trim {
+# This asciinema will show you the installation of borg as a standalone binary. Usually you only need this if you want to have an up-to-date version of borg or no package is available for your distro/OS.
+
+# First, we need to download the version, we'd like to install…
+wget -q --show-progress https://github.com/borgbackup/borg/releases/download/1.1.0b6/borg-linux64
+# and do not forget the GPG signature…!
+wget -q --show-progress https://github.com/borgbackup/borg/releases/download/1.1.0b6/borg-linux64.asc
+
+# In this case, we have already imported the public key of a borg developer. So we only need to verify it:
+gpg --verify borg-linux64.asc
+# Okay, the binary is valid!
+
+# Now install it:
+sudo cp borg-linux64 /usr/local/bin/borg
+sudo chown root:root /usr/local/bin/borg
+# and make it executable…
+sudo chmod 755 /usr/local/bin/borg
+
+# Now check it: (possibly needs a terminal restart)
+borg -V
+
+# That's it! Check out the other screencasts to see how to actually use borgbackup.
+}]
+
+foreach line [split $script \n] {
+	send_user "$ "
+	send_user -h $line\n
+	spawn -noecho /bin/sh -c $line
+	expect eof
+}

docs/misc/asciinema/run-install.sh

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+{
+	gpg --recv-keys "6D5B EF9A DD20 7580 5747 B70F 9F88 FB52 FAF7 B393"
+} &> /dev/null  # Do not pollute the asciinema output.
+# The above redirection can be removed for troubleshhting
+
+expect /asciinema/install.tcl