Created Error Handling (markdown)

Error-Handling.md

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+# Error Handling
+
+pgx uses Go 1.13+ style error wrapping. That means that `errors.Is()` and `errors.As()` should be used instead of directly testing an error for equality or attempting a type assertion.
+
+If an error is returned from PostgreSQL then underlying error type will be a [*pgconn.PgError](https://pkg.go.dev/github.com/jackc/pgconn?tab=doc#PgError).
+
+```go
+err = conn.QueryRow(context.Background(), "select 1 +").Scan(&greeting)
+if err != nil {
+  var pgErr *pgconn.PgError
+  if errors.As(err, &pgErr) {
+    fmt.Println(pgErr.Message) // => syntax error at end of input
+    fmt.Println(pgErr.Code) // => 42601
+  }
+}
+```