feat: added --preserve in the docs

docs/src/commands/update.md

@@ -17,3 +17,13 @@ ewwii update --inject "VAR1=bar,VAR2=foo2"
 # or in short
 ewwii update -i "VAR1=baz,VAR2=zoo"
 ```
+
+## Preserving updates with `--preserve`
+
+When you inject variables, the state is only updated temporarily. That means that if some other poll/listen variable triggered a update, your update will get overridden. So, this is why the `--preserve` flag exists. This flag allows you to preserve the variables in memory until it's overridden.
+
+```bash
+ewwii update -i "foo=hello" --preserve
+# or in short
+ewwii update -i "foo=hello" -p
+```