Update DEVELOPMENT.md (#193)

DEVELOPMENT.md

@@ -7,6 +7,7 @@ This library is developed by MultiSafepay to support multiple PHP-based e-commer
     - A section `## [Unreleased]` is kept in the top at all times.
     - New PRs are added via lines under `## [Unreleased]` while making a reference to the PR number or URL
 2) To make a new release, the lines under `## [Unreleased]` are copied into a new release section (`## [1.0.0] - 2001-01-01`), following the semantic versioning standard: Third digit increases with bug fixes, second digit (minor) increases with new features, first digit (major) increases with backward incompatibility changes.
-3) The `version` in the `composer.json` is changed with the new version.
-4) A new release is created in GitHub manually.
-5) The new release is copied from the internal repository to the public repository.
+3) The constant `SDK_VERSION` in the class `MultiSafepay\Util\Version` needs to be updated with the new version.
+4) The `version` in the `composer.json` is changed with the new version.
+5) A new release is created in GitHub manually.
+6) The new release is copied from the internal repository to the public repository.