doc: install: update TM note plus minor fixes

[greg-fer]

Updated the note about Toolchain Manager.
Applied minor fixes to different areas.
NCSDK-29557.

[NordicBuilder]

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Build number: 1

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Enabled	Name	Description
	ci-disabled	Disable the ci execution
	ci-all-test	Run all of ci, no test spec filtering will be done
	ci-force-downstream	Force execution of downstream even if twister fails
	ci-run-twister	Force run twister
	ci-run-zephyr-twister	Force run zephyr twister

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Toolchain

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Build docker image:

Test Spec & Results: ✅ Success; ❌ Failure; 🟠 Queued; 🟡 Progress; ◻️ Skipped; ⚠️ Quarantine

• ◻️ Toolchain
• ◻️ Build twister
• ◻️ Integration tests

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