Improve notation download and installation instructions

[toddysm]

The only installation experience that Notation currently has is for users to download the binary and manually copy to the appropriate folder on their machine. At a minimum, we need to provide the right instructions how to download, verify the binaries, and the correct places to copy the binaries for various operating systems.

Starting a HackMD spec for that on https://hackmd.io/@toddysm/SJhUuI7Bi

Related information is available in https://github.com/notaryproject/notation/blob/main/specs/directory.md

@zr-msft to prepare an article

[zr-msft]

thanks @toddysm feel free to assign to me

[zr-msft]

@FeynmanZhou @shizhMSFT @yizha1

are NOTATION_LIBEXEC, NOTATION_CONFIG, and NOTATION_CACHE directories created automatically after the CLI binary installed and executed? Do users need to set those environment variables or is it optional?

[FeynmanZhou]

@FeynmanZhou @shizhMSFT @yizha1

are NOTATION_LIBEXEC, NOTATION_CONFIG, and NOTATION_CACHE directories created automatically after the CLI binary installed and executed? Do users need to set those environment variables or is it optional?

@zr-msft
In general, notation cert add will create ~/.config/notation/truststore so users don't need to create NOTATION_LIBEXEC, NOTATION_CONFIG after they add a cert using Notation.

NOTATION_CACHE was desecrated in Beta.1 so we can ignore it.

We are updating and migrating this guide from notation repo to the website repo, you can find the updated version here.

[zr-msft]

Thank you @FeynmanZhou

I'll review/sign-off the linked PR and wait for merge to update my PR.

[zr-msft]

I'll need to make updates after #80 is merged. @FeynmanZhou @toddysm @dtzar you're welcome to merge now and I'll do a fast follow PR, otherwise will updated after #80 is merged.

[dtzar]

Merged @zr-msft

[zr-msft]

thank you @dtzar for merging. PR is updated to include links to new docs for more details on notation config