Update version release documentation

[DawoudSheraz]

In Tutor docs about releasing a new version https://docs.tutor.edly.io/tutor.html#releasing-a-new-version, the steps mentioned focus on updating version, adding changelog, and committing the change to upstream. These steps are a little outdated and need to be updated. In practice, the version upgrade happens in two phases:

1. Add changes and generate individual changelog
2. Update version and compile changelogs

Add changes and generate individual changelog
run make changelog-entry command - It will create changelog entries in a folder named changelog.d .
Commit and merge all the changes. e.g this commit.

Update version and compile changelogs
run make changelog command - It will delete all previous changelog entries from changelog.d folder and will add records of those entries to CHANGELOG.md file. The version is bumped in this commit.
merge your commit.
e.g. this commit.