doc: create upgrading section (#5310)

Signed-off-by: Rodrigo Kellermann <kellermann@gmail.com>

docs/introduction/stability-support.md

@@ -36,6 +36,24 @@ As of version 0.14.x , this is the only kubernetes version that we will guarante
 | 0.4.x       | 1.16 → 1.24        | Feb 2, 2022    | Oct 9, 2022     |
 | 0.3.x       | 1.16 → 1.24        | Jul 25, 2021   | Apr 6, 2022     |
 
+## Upgrading
+
+External Secrets Operator has not reached stable 1.0 yet. This means that **we treat each minor version bump as a potentially breaking change**. Breaking changes may include:
+
+- API schema changes
+- Default behavior modifications
+- Deprecated feature removals
+- Provider authentication changes
+- Configuration format updates
+
+**Important upgrade recommendations:**
+
+1. **Plan your upgrades carefully** - Always review release notes before upgrading, it could contain breaking changes information
+2. **Upgrade version by version** - We strongly recommend upgrading one minor version at a time (e.g., 0.18.x → 0.19.x → 0.20.x) rather than skipping versions
+3. **Test in non-production first** - Always validate upgrades in development/staging environments
+
+Until we reach v1.0, please treat minor version upgrades with the same caution you would give to major version upgrades in other projects.
+
 ## Provider Stability and Support Level
 
 The following table describes the stability level of each provider and who's responsible.