docs: update pip install to use sphinxcontrib-verilog-diagrams

[oharboe]

I'm unsure why the pip module is called sphinxcontrib-verilog-diagrams and elsewhere sphinx_hdl_diagrams is used. Historical resasons?

Anyway, now docs match what I find on pypi:

[mithro]

Yes, the module was originally only able to handle verilog code, but then some people improved it to support vhdl and other things that Yosys can parse.

[mithro]

We should probably create a "dummy" sphinxcontrib-verilog-diagrams module which just redirects everything to sphinxcontrib-hdl-diagrams?

[mithro]

I'll also upload the module to PyPi as sphinxcontrib-hdl-diagrams

[mithro]

#93

[oharboe]

@mithro I'm trusting your judgement here :-) I saw something that I thought was a simple search and replace fix...

Close this PR?

[mithro]

Yes, closing the pull request.

Also logged #94