create changelog file if it does not exist

[usernam3]

When meta_commit changelog is called and CHANGELOG.md does not exist in the directory, it shows error :

meta_commit/lib/meta_commit/changelog/adapters/changelog.rb:70:in `read': No such file or directory @ rb_sysopen - CHANGELOG.md (Errno::ENOENT)

It would be better if meta_commit will create the CHANGELOG.md (if it is missing) and notify the user about it.

Scenario that should pass when this issue is closed (add it to features/changelog_command.feature)

Scenario: Run command on repository without changelog file
    Given three_commits_with_two_tags git repository
    When I run meta_commit command `changelog v1.0 v2.0`
    Then the output should contain #{notification_that_file_created}
    Then the output should contain exactly "added version [v2.0] to CHANGELOG.md"
    Then the changelog should be equal to fixture file "three_commits_with_tags"

[usernam3]

• Add new scenario to feature (features/changelog_command.feature)
• Run (rake features) and see it fails
• Handle the error (Maybe on cli.rb:29 level, create file if it doesn't exist)
• See usage scenario is passing 💪