[BEAM-6918] Changed github link to not require login and fixed broken example link

[davidyan74]

1. git clone git@github.com:apache/beam.git requires the user to be logged in, while https://github.com/apache/beam does not.
2. Spaces in the example link need to be escaped.

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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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[davidyan74]

R: @qinyeli

[qinyeli]

Thanks, David. I can't merge the PR, though, as I am not a Beam commiter.

R: @pabloem Would you be able to review this?

[pabloem]

Done! Thanks!