Update soak results page

+ Link to methodology (instead telling readers to search there).
+ Explain low amount of test results shown.
+ Clarify that y-axis shows an estimated interval (not direct measurement).

Change-Id: I4d9132fa102624a38d52f0e52dd12e834bd1350f
Signed-off-by: Vratko Polak <vrpolak@cisco.com>