Please make the branch name variable available in PR Template

[전지원]

I want to insert the following command onto PR Template.

```shell
BRANCH={{branch_name}}; git fetch origin $BRANCH; git pull; git checkout $BRANCH;
```

To achieve this, a new variable including branch name must be created.

[Theodora Boudale · Accepted solution]

Hi @전지원,

You can use the special variables {{source_branch}} and {{destination_branch}} in the Default pull request description in order to refer to the PR's branches.

I will ask the team that maintains the documentation to update our docs and include these variables as well.

Please feel free to reach out if you have any questions.

Kind regards,
Theodora

[전지원]

Thanks for your support!