[DOCS] Typo in installation guide URL

[marekkrk]

Description
The URL to Salt installation guide contains a double slash: "https://github.com/saltstack//salt-install-guide"

Suggested Fix
The URL should contain a single slash.

Type of documentation
Salt documentation (website)

Location or format of documentation
https://docs.saltproject.io/salt/install-guide/en/latest/

Additional context
n/a

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