Installation docs fixes

[kobigurk]

1. pd requires clang to be installed to compile librocksdb-sys, missing from linux instructions in https://guide.penumbra.zone/main/pcli/install.html.

2. weird latexing going on here:

3. missing $ sign in

4. Also in

[hdevalence]

I wonder whether the weird LaTeX behavior is related to the missing $ signs?

[zbuc]

@hdevalence I fixed the same issue on some of the other documentation pages but missed this -- katex is parsing any $ as a LaTeX special character and adding the span tags. The fix is that literal $ characters in documentation always need to be escaped: \$

[hdevalence]

Hmm, even in code blocks ? That seems pretty suboptimal

[zbuc]

Yep. I tested locally and if I didn't have mdbook-katex installed, literal $ within a code block worked fine, but as soon as I installed mdbook-katex it'd need to be escaped.