Add Watch The Difference as a zsh til.

README.md

@@ -159,6 +159,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Saying Yes](zsh/saying-yes.md)
 - [Search History](zsh/search-history.md)
 - [Switch Versions of a Brew Formula](zsh/switch-versions-of-a-brew-formula.md)
+- [Watch The Difference](zsh/watch-the-difference.md)
 - [Watch This Run Repeatedly](zsh/watch-this-run-repeatedly.md)
 - [Where Are The Binaries?](zsh/where-are-the-binaries.md)
 

zsh/watch-the-difference.md

@@ -0,0 +1,15 @@
+# Watch The Difference
+
+The `watch` command is a simple way to repeatedly run a particular command.
+I'll sometimes use it to monitor the response from some endpoint. `watch`
+can make monitoring responses even easier when the `-d` flag is employed.
+This flag instructs `watch` to highlight the parts of the output that are
+*different* from the previous run of the command.
+
+So if I run
+
+```
+$ watch -d curl -LIs localhost:3000
+```
+
+I can easily see if the http status of the request changes.