[Doc] Add how to set environment variables for fish users (#1800)
[Doc] Add how to set environment variables for fish users (#1800)

* [doc]: Add how to set environment variables for fish users

* [doc] shorten the description for fish users

* [doc] enclose fish descriptions with note

Co-authored-by: 彭于斌 <2430f41068eeee88e52afd712d0bb273833fdbfe@qq.com>

Co-authored-by: 彭于斌 <2430f41068eeee88e52afd712d0bb273833fdbfe@qq.com>
yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi