add more examples to tr

These examples were suggested to add and are based from the tr-wikipedia article at https://en.wikipedia.org/w/index.php?title=Tr_(Unix)&oldid=631477596

pages/common/tr.md

@@ -1,15 +1,27 @@
 # tr
 
-> translate characters - run replacements based on single characters
+> translate characters - run replacements based on single characters and character sets
 
-- replace all occurrences of a character in a file, and print the result
+- Replace all occurrences of a character in a file, and prints the result
 
-`tr {{find_character}} {{replace_character}} < {{filename}}`
+`tr {{find_characters}} {{replace_characters}} < {{filename}}`
 
- Translate the contents of the file to upper-case, prints result.
+- Maps each character of the first set to the corresponding character of the second set.
+
+`tr 'abcd' 'jkmn' < {{filename}}`
+
+- Delete all occurances of the specified set of characters from the input.
+
+`tr -d '{{input_characters}}'`
+
+- Compresses a series of identical characters to a single character.
+
+`tr -s '\n'`
+
+- Translate the contents of the file to upper-case, prints result.
 
 `tr "[:lower:]" "[:upper:]" < {{filename}}`
 
-Strip out non-printable characters from the file, prints result.
+- Strip out non-printable characters from the file, prints result.
 
 `tr -cd "[:print:]" < {{filename}}`