Documentation/upgrades: highlight wal, embed changes

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

CHANGELOG-3.4.md

@@ -67,7 +67,7 @@ See [code changes](https://github.com/coreos/etcd/compare/v3.3.0...v3.4.0) and [
 - Change [`wal` package function signatures](https://github.com/coreos/etcd/pull/9572) to support [structured logger and logging to file](https://github.com/coreos/etcd/issues/9438) in server-side.
   - Previously, `Open(dirpath string, snap walpb.Snapshot) (*WAL, error)`, now `Open(lg *zap.Logger, dirpath string, snap walpb.Snapshot) (*WAL, error)`.
   - Previously, `OpenForRead(dirpath string, snap walpb.Snapshot) (*WAL, error)`, now `OpenForRead(lg *zap.Logger, dirpath string, snap walpb.Snapshot) (*WAL, error)`.
-  - Previously, `Repair(dirpath string) bool` now `Repair(lg *zap.Logger, dirpath string) bool`.
+  - Previously, `Repair(dirpath string) bool`, now `Repair(lg *zap.Logger, dirpath string) bool`.
   - Previously, `Create(dirpath string, metadata []byte) (*WAL, error)`, now `Create(lg *zap.Logger, dirpath string, metadata []byte) (*WAL, error)`.
 - Remove [`embed.Config.SetupLogging`](https://github.com/coreos/etcd/pull/9572).
   - Now logger is set up automatically based on [`embed.Config.Logger`, `embed.Config.LogOutput`, `embed.Config.Debug` fields](https://github.com/coreos/etcd/pull/9572).

Documentation/upgrades/upgrade_3_4.md

@@ -26,7 +26,7 @@ Highlighted breaking changes in 3.4.
 +etcd --peer-trusted-ca-file ca-peer.crt
 ```
 
-#### Change in ``pkg/transport`
+#### Change in `pkg/transport`
 
 Deprecated `pkg/transport.TLSInfo.CAFile` field.
 
@@ -45,6 +45,40 @@ if err != nil {
 }
 ```
 
+#### Change in `wal`
+
+Changed `wal` function signatures to support structured logger.
+
+```diff
+import "github.com/coreos/etcd/wal"
++import "go.uber.org/zap"
+
++lg, _ = zap.NewProduction()
+
+-wal.Open(dirpath, snap)
++wal.Open(lg, dirpath, snap)
+
+-wal.OpenForRead(dirpath, snap)
++wal.OpenForRead(lg, dirpath, snap)
+
+-wal.Repair(dirpath)
++wal.Repair(lg, dirpath)
+
+-wal.Create(dirpath, metadata)
++wal.Create(lg, dirpath, metadata)
+```
+
+#### Change in `embed.Etcd`
+
+`embed.Config.SetupLogging` has been removed in order to prevent wrong logging configuration, and now set up automatically.
+
+```diff
+import "github.com/coreos/etcd/embed"
+
+cfg := &embed.Config{Debug: false}
+-cfg.SetupLogging()
+```
+
 ### Server upgrade checklists
 
 #### Upgrade requirements