[PATCH v5 4/4] doc: added description of `IMAGE_TRANSIENT_PACKAGES`

[claudius.heine.ext@siemens.com]

From: Claudius Heine <ch@denx.de>

---
 doc/user_manual.md | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/doc/user_manual.md b/doc/user_manual.md
index a2f4b92..91f9a6d 100644
--- a/doc/user_manual.md
+++ b/doc/user_manual.md
@@ -481,6 +481,22 @@ Isar contains two image type classes that can be used as reference:
 
 ---
 
+## Customize and configure image
+
+Customization and configuration of an image should be done via packages, see below.
+
+Adding those configuration packages to the image can be done in two ways:
+
+ 1. Simply adding the package to `IMAGE_INSTALL`, like any other isar created package, or
+ 2. Adding the package to `IMAGE_TRANSIENT_PACKAGES`.
+
+In most cases adding the configuration package to `IMAGE_INSTALL` is the right option.
+
+In cases were the configuration script of the package has some external dependencies, that should not be part of the final image, then `IMAGE_TRANSIENT_PACKAGES` is the right option.
+Packages in the `IMAGE_TRANSIENT_PACKAGES` variable are installed to the image and purged in the next step. If such a configuration package deploys file as part of their content, then those files will be removed as well.
+
+---
+
 ## Add a Custom Application
 
 Before creating a new recipe it's highly recommended to take a look into the BitBake user manual mentioned in Terms and Definitions section.
-- 
2.17.0