[DOCS] fix get context instructions

[itaise]

Changes proposed in this pull request:

• get_context doesn't take any parameters, so I changed the instructions to another way that can initialize data context from a path

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🔨 Latest commit	b114508ac47fefdb512fb5ac0a1b9a3e33da746c

[anthonyburdi]

Will be fixed in https://github.com/great-expectations/great_expectations/pull/7417