Update pipeline documentation

[tteggelit]

This:

• Adds a new Basics section to introduce a typical Ramble workspace workflow and the concepts of pipelines and phases
• Updates the Advanced section on pipelines with more information and diagrams to help explain the flow
• Updates the docs conf.py for graphviz to remove global rank direction and sets the fonts to something less Mac specific

Attaching PDFs of the new pages to make it a bit easier to see the results without people needing to checkout my branch and run Sphinx against it.
Basics - Pipelines and Phases.pdf
Advanced - Pipelines and Builtins.pdf

[gemini-code-assist]

Code Review

This pull request significantly expands and restructures the documentation regarding Ramble's pipelines and phases. It introduces a new pipelines.rst file detailing common workspace workflows, updates advanced_topics.rst with architectural overviews and phase graphs, integrates Graphviz diagrams to visualize these workflows, and updates Sphinx configuration settings. The review feedback suggests minor grammatical and phrasing corrections to improve readability, such as removing a redundant "below", correcting "usecases" to "use cases", and adding a missing article.