doc: Add chapter for state overrides

doc/07-State-Overrides.md

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+# State Overrides
+
+Business processes utilize their children's states to calculate their own state.
+While you can influence this with [operators](09-Operators.md), it's also possible
+to override individual states. (Currently this applies only to service nodes.)
+
+## Configuring Overrides
+
+State overrides get configured per node. When adding or editing a node, you can
+define which state should be overridden with another one.
+
+Below `WARNING` is chosen as a replacement for `CRITICAL`.
+
+![Service State Override Configuration](screenshot/07_state_overrides/0701_override_config.png "Service State Override Configuration")
+
+## Identifying Overrides
+
+In tile view overridden states are indicated by an additional state ball in the
+lower left of a tile. This is then the actual state the object is in.
+
+![Overridden Tile State](screenshot/07_state_overrides/0702_overridden_tile.png "Overridden Tile State")
+
+In tree view overridden states are indicated on the very right of a row. There
+the actual state is shown and which one it is replaced with.
+
+![Overridden Tree State](screenshot/07_state_overrides/0703_overridden_tree.png "Overridden Tree State")
+
+## File Format Extensions
+
+The configuration file format has slightly been changed to accommodate state
+overrides. Though, previous configurations are perfectly upwards compatible.
+
+### New Extra Line
+
+For process nodes a new extra line is used to store state overrides.
+
+```
+state_overrides dev_database_servers!mysql;mysql|2-1
+```
+
+The full syntax for this is as follows:
+
+```
+state_overrides <process>!<child>|n-n[!<child>|n-n[,n-n]]
+```