Include note of common profiling issue

[tbillington]

• Includes a note about a common issue seen when profiling with span based tracing tools
• Adds a table of contents to profile.md

Rendered.

Suggested by Jasmine on discord.

[github-actions]

Example alien_cake_addict failed to run, please try running it locally and check the result.

[alice-i-cecile]

This is a nice improvement! Both the common issue and the cleanup are nice.

[JMS55]

Thanks for writing this! Some minor wording changes and then we're good to go.

[mockersf]

You need to increase all your heading levels by 1, there can be only one #-level heading.

The linter is also unhappy about your note: https://github.com/updownpress/markdown-lint/blob/master/rules/036-no-emphasis-as-header.md

[mockersf]

it seems it's the first time the linter passed on this file, and it's unhappy with the list made with *, could you replace it with -?

[tbillington]

I was following the patterns in https://raw.githubusercontent.com/bevyengine/bevy/v0.11.2/examples/README.md.

Will update them in the morning, didn't know about the markdown linter, thanks!