Add migration guide

Author: alamb

changelog/0.55.0.md

@@ -21,6 +21,27 @@ under the License.
 
 This release consists of 55 commits from 25 contributors. See credits at the end of this changelog for more information.
 
+## Migrating usages of `Expr::Value`
+
+In v0.55, sqlparser the `Expr::Value` enum variant contains a `ValueWithSpan` instead of a `Value`. Here is how to migrate.
+
+### When pattern matching
+
+```diff
+- Expr::Value(Value::SingleQuotedString(my_string)) => { ... }
++ Expr::Value(ValueWithSpan{ value: Value::SingleQuotedString(my_string), span: _ }) => { ... }
+```
+
+### When creating an `Expr`
+
+Use the new `Expr::value` method (notice the lowercase `v`), which will create a `ValueWithSpan` containing an empty span :
+
+```diff
+- Expr::Value(Value::SingleQuotedString(my_string))
++ Expr::value(Value::SingleQuotedString(my_string))
+```
+
+
 **Breaking changes:**
 
 - Enhance object name path segments [#1539](https://github.com/apache/datafusion-sqlparser-rs/pull/1539) (ayman-sigma)