Update cheatsheets

pio-system

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# pio system
+
+> Miscellaneous system commands for PlatformIO.
+> More information: <https://docs.platformio.org/en/latest/core/userguide/system/>.
+
+- Install shell completion for the current shell (supports Bash, Fish, Zsh and PowerShell):
+
+`pio system completion install`
+
+- Uninstall shell completion for the current shell:
+
+`pio system completion uninstall`
+
+- Display system-wide PlatformIO information:
+
+`pio system info`
+
+- Remove unused PlatformIO data:
+
+`pio system prune`
+
+- Remove only cached data:
+
+`pio system prune --cache`
+
+- List unused PlatformIO data that would be removed but do not actually remove it:
+
+`pio system prune --dry-run`