RDKBDEV-3334:Add Wan Manager Documentation

[Ashrafbhanu-k]

RDKBDEV-3334
Reason for Change:
To add Component Documentation for Wan Manager component. Added README under new folder ./docs
Fix:
Added the documentation
Test Procedure:
None
Signed-off-by: Ashrafbhanu-k [Ashraf_bhanu@comcast.com]

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[kartikg33]

@guto86 @S-Parthiban-Selvaraj is it worth building the /docs folder into a wiki?
Please take a look at what we've done for meta-rdk-broadband-apps

Wiki is here: https://rdkcentral.github.io/meta-rdk-broadband-apps/