[Buildroot] [RFC 1/2] docs/manual/migrating.txt: add section with general migrating tips

[Arnout Vandecappelle (Essensium/Mind)]

This is based on Arnout's experience with migrating Buildroot.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>
---
 docs/manual/migrating.txt | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/docs/manual/migrating.txt b/docs/manual/migrating.txt
index 92e487c71e..9fd7d7e676 100644
--- a/docs/manual/migrating.txt
+++ b/docs/manual/migrating.txt
@@ -8,6 +8,34 @@ Some versions have introduced backward incompatibilities. This section
 explains those incompatibilities, and for each explains what to do to
 complete the migration.
 
+[[migrating-approach]]
+=== General approach
+
+To migrate from an older Buildroot version, take the following steps.
+
+. For all your configurations, do a build in the old Buildroot
+  environment. Save the full +.config+ and
+  +build/packages-file-list.txt+.
+. Review the specific migration notes below and make the required
+  adaptations to external packages and custom build scripts.
+. In the new Buildroot environment, run +make menuconfig+ starting from
+  the existing +.config+.
+. If anything is enabled in the Legacy menu, check its help text,
+  unselect it, and save the configuration.
+. Review the CHANGES file to see if any of your packages and features
+  are affected by the changes.
+. Build in the new Buildroot environment.
+. Fix build issues in external packages (usually due to updated
+  dependencies).
+. Compare the new +packages-file-list.txt+ with the original one, to
+  check if no required files have disappeared.
+. For configuration (and other) files in a custom overlay that overwrite
+  files created by Buildroot, check if there are changes in the
+  Buildroot-generated file that need to be propagated to your custom
+  file.
+. Run +make savedefconfig+ and verify that what is selected really is
+  what you intended to enable.
+
 [[br2-external-converting]]
 === Migrating to 2016.11
 
-- 
2.31.1