[Website] Change home page heading text to match GitHub repo description

In May there was a discussion on the Arrow dev mailing list about shortening the description of Apache Arrow that appears on its GitHub repo page. The discussion is archived at https://lists.apache.org/thread.html/rccd9848550e4b606ff80295d152419e4c5486a7be14e239ee21c53fd%40%3Cdev.arrow.apache.org%3E.

The outcome of this was that the description was changed from

Apache Arrow is a cross-language development platform for in-memory
data. It specifies a standardized language-independent columnar memory
format for flat and hierarchical data, organized for efficient
analytic operations on modern hardware. It also provides computational
libraries and zero-copy streaming messaging and interprocess
communication…

to

Apache Arrow is a multi-language toolbox for accelerated data interchange and in-memory processing

I think we should change the heading text on https://arrow.apache.org to match this new description in the GitHub repo. The goal here is not to make the website heading text shorter, but to be more consistent.

Currently the website heading text reads:

A cross-language development platform for in-memory analytics

I think we should change it to:

A multi-language toolbox for accelerated data interchange and in-memory processing