Adding section in usage docs for setting custom timeout (#149)

* Adding section for setting custom timeout

* Minor word change

* Addressing PR feedback

Co-authored-by: Kyle W. Rader <kyle.rader@microsoft.com>

Co-authored-by: Kyle W. Rader <kyle.rader@microsoft.com>

Author: Haard30

docs/usage.md

@@ -96,6 +96,14 @@ Use the option `--output` to get the token in the desired formats. Available cho
 3. `--output status` returns the status of the authentication and the cache.
 4. `--output none` returns nothing.
 
+## Setting custom timeout
+Azureauth defaults to a 15 minute timeout. You can override this with a custom timeout value using `--timeout`. The value is interpreted as a decimal number of minutes. The example below will wait 10 minutes and 45 seconds.
+
+Usage:
+```
+azureauth --alias alias1 --timeout 10.75
+```
+
 Use the command `azureauth --help` to understand more available options.
 
 ### Examples