docs: add quotation to pip install

[younesStrittmatter]

pip install example[example] doesn't work in all shells but pip install "example[example]" works consistently.

[github-actions]

This PR causes the following changes to the html docs (ubuntu-latest-3.11):

diff -r docs-base/_sources/index.rst.txt docs-head/_sources/index.rst.txt
214c214
<     pip install psyneulink[tutorial]
---
>     pip install "psyneulink[tutorial]"
220c220
<     pip install .[tutorial]
---
>     pip install ".[tutorial]"
diff -r docs-base/index.html docs-head/index.html
365c365
< <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="n">psyneulink</span><span class="p">[</span><span class="n">tutorial</span><span class="p">]</span>
---
> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="s2">&quot;psyneulink[tutorial]&quot;</span>
369c369
< <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="o">.</span><span class="p">[</span><span class="n">tutorial</span><span class="p">]</span>
---
> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="s2">&quot;.[tutorial]&quot;</span>

...

See CI logs for the full diff.

[github-actions]

This PR causes the following changes to the html docs (ubuntu-latest-3.11):

diff -r docs-base/_sources/index.rst.txt docs-head/_sources/index.rst.txt
214c214
<     pip install psyneulink[tutorial]
---
>     pip install "psyneulink[tutorial]"
220c220
<     pip install .[tutorial]
---
>     pip install ".[tutorial]"
diff -r docs-base/index.html docs-head/index.html
365c365
< <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="n">psyneulink</span><span class="p">[</span><span class="n">tutorial</span><span class="p">]</span>
---
> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="s2">&quot;psyneulink[tutorial]&quot;</span>
369c369
< <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="o">.</span><span class="p">[</span><span class="n">tutorial</span><span class="p">]</span>
---
> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="s2">&quot;.[tutorial]&quot;</span>

...

See CI logs for the full diff.

[kmantel]

Thanks!