Matlab novice material review

Update lesson 1 and 2
Sure.

We have this line:
> All we need to do is to define a start value, a [stride](../../gloss.html#stride),
> and an end value.

And later, this one:
> We don't have to take all the values in the slice---if we provide a stride.

Since we're not really introducing strides the first time, how about something along these lines:

"The `:` (colon) operator can also be used to select multiple rows, if we
define a start value and end value for the first dimension:"

...

"and similarly, multiple columns, by defining start and end values for the *second* dimension"

...