Add SBCONFIG_PORT to documentation

[pierrecholhot]

According to the docs, the following is the default method to run the storybook:

start-storybook -p 5700

However, I stumbled upon this undocumented SBCONFIG_PORT environment variable in the code while looking for a way to run the storybook remotely on a specific port defined as an ENV_VAR.

It turns out I can start the server this way, without specifying the port with -p:

export SBCONFIG_PORT=5700
start-storybook

Is it recommended to use SBCONFIG_PORT ? If so, it could be useful to find a mention of this in the docs.

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As a side note, I edited my init script to use this environment variable only if it's set, otherwise, fallback to the default hardcoded. The reason is to be able to set a different PORT on a remote env without having to EXPORT one locally.

start-storybook -p ${SBCONFIG_PORT:-5700}

[arunoda]

SBCONFIG_PORT is something we did for some internal tooling.
It's never meant for public use.
We may remove it in the future.