docs: fix typo in introduction

[changsun20]

📝 Description

This PR fixes a small typo in the introduction part.

• [1 2 "three"] or (list 1 2 "three") - a vector of values with index (random access)
• [1 2 "three"] or (vector 1 2 "three") - a vector of values with index (random access)

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[changsun20]

Thanks!