fix(github docs): Includes @angular/cdk in installation instructions

[julianobrasil]

Includes @angular/cdk in installation instructions.

Closes #5552.

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[julianobrasil]

I signed it!

[googlebot]

CLAs look good, thanks!

[julianobrasil]

Just updated this PR as said in #5552 (comment)

[jelbourn]

LGTM

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