Update readme
Handle invalid URLs slightly better

Now, we just don't do anything when an invalid URL is passed.
Eventually we'd like a TOAST message or some text to be displayed, but
for now this is better than a crash.

Also set the Y axis to an appropriate scale. Again this can be done
better, but for the time being this is sufficient.

Signed-off-by: Prashant Malani <p.malani@gmail.com>
Add humidity data graph

Add support for humidity data. We also add support for timestamps along
the X axis, so that the data is scaled correctly with respect to time.

Also add legend support, so that both graph's can be distinguished more
easily.
Merge branch 'master' into sensor