add description and example of sponge

README.md

@@ -247,6 +247,18 @@ A few examples of piecing together commands:
       awk '{ x += $3 } END { print x }' myfile
 ```
 
+- `sponge`: from moreutils -  soak up standard input and write to a file. I you want to change a file that is the source of a pipline: Instead of:
+```bash
+cat file | sort | uniq  | iconv -f utf8 -t latin1 > /tmp/file && mv /tmp/file file
+```
+
+You can do:
+
+```bash
+cat file | sort | uniq  | iconv -f utf8 -t latin1 | sponge file
+```
+
+
 - If want to see sizes/dates on a tree of files, this is like a recursive `ls -l` but is easier to read than `ls -lR`:
 ```sh
       find . -type f -ls