Update install instructions to make compatible with zsh

[DomonkosCs]

I've recently tried to install StoneSoup using the provided python -m pip install -e .[dev] command, and it didn't work. I've found out, that when using zsh, the location and the extra have to be enclosed by quotation marks. For the sake of other zsh users, I think a quick instruction could be given in the docs.

[codecov[bot]]

Codecov Report

Merging #697 (542e718) into main (24fd8de) will not change coverage. The diff coverage is n/a.

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##             main     #697   +/-   ##
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  Coverage   94.59%   94.59%           
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  Files         171      171           
  Lines        8619     8619           
  Branches     1666     1666           
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  Hits         8153     8153           
  Misses        341      341           
  Partials      125      125           

Flag	Coverage Δ
integration	69.26% <ø> (+0.02%)	:arrow_up:
unittests	92.13% <ø> (ø)

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[sdhiscocks]

Thanks @DomonkosCs. I think to keep things simple, we could just have the quotations marks adding to the original command, as that'll then make that one command compatible with all.

[DomonkosCs]

Ok, good idea!