[docs] Improve getting started guide (#252)

* Update Readme & improve md layout

- ESPHome now supports LibreTiny natively
- Added extra PIO docs references
- Reworded some sections slightly, to accomodate proper grammar
- PIO deprecated the `platformio platform install` command, replaced this with the official recommendation/replacement

* Use backslash for line break, revert changing indent

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Co-authored-by: Kuba Szczodrzyński <kuba@szczodrzynski.pl>

mkdocs.yml

@@ -67,6 +67,8 @@ markdown_extensions:
       anchor_linenums: true
   - pymdownx.tabbed:
       alternate_style: true
+  - pymdownx.escapeall:
+      hardbreak: true
   - pymdownx.inlinehilite
   - pymdownx.details
   - pymdownx.superfences