[PATCH 2/2][kteam-tools] cranky/docs: add documentation for new chroot update subcommand

[Zachary Tahenakos]

Signed-off-by: Zachary Tahenakos <zachary.tahenakos at canonical.com>
---
 cranky/docs/cranking-the-kernel.md | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/cranky/docs/cranking-the-kernel.md b/cranky/docs/cranking-the-kernel.md
index 7c0f54bf..52e0ae5e 100644
--- a/cranky/docs/cranking-the-kernel.md
+++ b/cranky/docs/cranking-the-kernel.md
@@ -63,6 +63,21 @@ cranky chroot create-base xenial:linux
 cranky chroot create-session configs xenial:linux
 ```
 
+# Updating the chroot
+<!--cheatsheet-->
+```
+cranky chroot update RELEASE:linux
+```
+<!--/cheatsheet-->
+
+For a chroot that already exists, ensure that it is up to date by running cranky chroot update before performing the crank.
+
+Example:
+```
+cranky chroot update xenial:linux
+```
+
+
 ## Build
 
 ### Update the kteam-tools repo
-- 
2.25.1