Remove non-existing fromString from README API doc
Remove non-existing fromString from README API doc

This commit removes the API documentation for the fromString Cloudevent
function as it does not seem to exist.

Signed-off-by: Daniel Bevenius <ae63d1d4d7994483a3e520cafec7a829fe25c0a1@gmail.com>

cloudevents/sdk-javascript,cloudevents/sdk-javascript