[ITensors] [Docs] θ as parameter name in Rz and CRz gates rather than ϕ

[terasakisatoshi]

Description

When I read code in qubit.jl I found we are supposed to specify keyword arugment θ when creating a Rz (similarly CRz).

The current documentation says "Rz" (takes argument: ϕ), which is not consistent with code in here (similarly CRz).

How Has This Been Tested?

Generate docs locally with the following commands:

$ cd /path/to/ITensors.jl
$ julia --project=docs -e 'using Pkg; Pkg.instantiate()'
$ julia --project=docs -e 'include("docs/make.jl")' 

It is followed by

$ using LiveServer; serve(dir="docs/build")

Checklist:

• My code follows the style guidelines of this project. Please run using JuliaFormatter; format(".") in the base directory of the repository (~/.julia/dev/ITensors) to format your code according to our style guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that verify the behavior of the changes I made.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.

[mtfishman]

Thanks!