sed: Added command for excluding lines while printing (#984)

Co-authored-by: Rico Sta. Cruz <rstacruz@users.noreply.github.com>

sed.md

@@ -6,36 +6,51 @@ intro: |
   Here's some hints on using sed.
 ---
 
-### In place replacements
+## In place replacements
 
-#### In GNU sed: use `-i` without arg.
+### In-place replacement (GNU)
 
 ```bash
 sed -i -e 's/foo/bar/' example.md
 ```
 
-#### In OSX, `-i ''` is required.
+In GNU sed: use `-i` without arg.
+
+#### In-place replacement (BSD)
 
 ```bash
 sed -i '' -e 's/foo/bar/' example.md
 ```
 
-### File regions
+ In OSX, `-i ''` is required.
 
-#### Print until a certain line is met
+## File regions
+{:.-three-column}
+
+### Print until a certain line is met
 
 ```bash
 sed '/begin api/q'
 ```
 
-#### Print until a certain line is met, but not that line
+### Print until a certain line is met, but not that line
 
 ```bash
 sed '/^# begin/,$d'
 ```
 
-#### Print everything after a given line
+### Print everything after a given line
 
 ```bash
 sed -n '/end api/,$p'
 ```
+
+Print after a given line is found.
+
+### Print everything except matching
+
+```bash
+sed -n '/regex/d;'
+```
+
+Print everything except lines matching regex. Useful for printing files with comments.