Added pacman notes to the knowledge base

knowledge base/pacman.md

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+# Pacman
+
+Useful options:
+
+- `--asdeps`
+- `--asexplicit`
+- `--needed`
+- `--unneeded`
+
+## TL;DR
+
+```shell
+
+# search an installed package
+pacman --query --search ddc
+
+# list all explicitly installed packages
+pacman --query --explicit
+
+# set a package as explicitly (manually) installed
+pacman --database --asexplicit dkms
+# set a package as installed as dependency (automatically installed)
+pacman --database --asdeps autoconf
+
+# install zsh unsupervisioned (useful in scrips)
+pacman --noconfirm \
+	--sync --needed --noprogressbar --quiet --refresh \
+	fzf zsh-completions
+# completely remove virtualbox-guest-utils-nox unsupervisioned (useful in scrips)
+pacman --noconfirm \
+	--remove --nosave --noprogressbar --quiet --recursive --unneeded \
+	virtualbox-guest-utils-nox
+```
+
+## Further readings
+
+- [Prevent pacman from reinstalling packages that were already installed]
+
+[Prevent pacman from reinstalling packages that were already installed]: https://superuser.com/questions/568967/prevent-pacman-from-reinstalling-packages-that-were-already-installed#568983