[BEAM-7417] Fix incorrect command on flink runner docs

[kaplanbora]

Flink application needs run command so it can start running.

Please add a meaningful description for your change here

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---	---	---	---	---
Java
Python		---			---	---	---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website
Non-portable
Portable	---		---	---

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[mxm]

Thanks for spotting this!