flexget: add page (#15023)

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Co-authored-by: Wiktor Perskawiec <git@spageektti.cc>
Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

pages/common/flexget.md

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+# flexget
+
+> A multipurpose automation tool for content like torrents, nzbs, podcasts, comics, series, movies, etc.
+> More information: <https://flexget.com/en/CLI>.
+
+- Run all Flexget tasks now:
+
+`flexget execute --now`
+
+- Start the Flexget daemon and daemonize its process:
+
+`flexget daemon start --daemonize`
+
+- List all series recorded in Flexget:
+
+`flexget series list`
+
+- Run a task from a config file:
+
+`flexget -c {{path/to/config.yml}} execute --task {{task_name}}`