Unify example READMEs to improve onboarding experience

[nikolausWest]

Update all example READMEs to follow the template set forth here: #5359 (comment) excluding the "Logging and Visualizing with Rerun" section.

As a part of achieving:

• Turn all in-repo Rust examples into mini-tutorials #5437
• Turn all in-repo C++ examples into mini-tutorials  #5436
• Turn all in-repo python examples into mini-tutorials #5435

We should do a pass over all example README's that end up as example detail pages on the website. This issue is about doing everything except the section with code snippets (that make it a mini-tutorial). The goal is to orient users around "what it is they are looking at" (an example of visualizing X with Rerun by logging data), and how to run the code. For external examples how to run the code can just refer to the external repository.

The goal is to make the examples more useful for people who are new to Rerun and are exploring what you can do with it.

See this (Rerun private) page for more context.

[nikolausWest]

These PR partially address this issue:

• Updated READMEs for examples: LLM Embedding-Based Named Entity Recognition, nuScenes, Objectron, Open Photogrammetry Format, Raw Mesh #5653
• Updated READMEs for the examples - Batch 1 #5620