Added sed's notes to the knowledge base

knowledge base/sed.md

@@ -0,0 +1,14 @@
+# SED
+
+## TL;DR
+
+```shell
+# Delete lines matching "OAM" from a file.
+sed -e '/OAM/d' -i .bash_history
+
+# Change fstab entries.
+sed /etc/fstab \
+  -e "s|#.*\s*/boot\s*.*|/dev/sda1  /boot  vfat   defaults             0 0|" \
+  -e "s|#.*\s*ext4\s*.*|/dev/sda2  /      btrfs  compress-force=zstd  0 0|" \
+  -e '/#.*\s*swap\s*.*/d'
+```