Create a Bengali (Bangla) translation of the open terminal guide

[devadvance]

Based on the English version of the guide (https://github.com/devadvance/terminalcheatsheet/blob/staging/guides/open-terminal-macos.md), create a Bengali (Bangla) translation in https://github.com/devadvance/terminalcheatsheet/blob/staging/i18n/bn/guides/open-terminal-macos.md.

You can copy this template to use a starting point: https://github.com/devadvance/terminalcheatsheet/blob/staging/i18n/new_language_templates/guides/open-terminal-macos.md

It is OK to use the English images/GIFs. Look for TODO in the file for suggested places for translations.

Please comment on this issue before starting work so people are informed that you are working on it.