Add coverage of watch.

Thanks to ShawnMilo!
Fixes #237
Fixes #241

README.md

@@ -293,6 +293,8 @@ A few examples of piecing together commands:
       cat access.log | egrep -o 'acct_id=[0-9]+' | cut -d= -f2 | sort | uniq -c | sort -rn
 ```
 
+- To continuously monitor changes, use `watch`, e.g. check changes to files in a directory with `watch -d -n 2 'ls -rtlh | tail'` or to network settings while troubleshooting your wifi settings with `watch -d -n 2 ifconfig`.
+
 - Run this function to get a random tip from this document (parses Markdown and extracts an item):
 ```sh
       function taocl() {
@@ -329,7 +331,7 @@ A few examples of piecing together commands:
 
 - `fold`: wrap lines of text
 
-- `column`: format text into columns or tables
+- `column`: format text into fixed-width columns or tables
 
 - `expand` and `unexpand`: convert between tabs and spaces
 
@@ -361,6 +363,8 @@ A few examples of piecing together commands:
 
 - `time`: execute and time a command
 
+- `watch`: run a command repeatedly, showing results and/or highlighting changes
+
 - `tac`: print files in reverse
 
 - `shuf`: random selection of lines from a file