Improve "Solutions" section description

[jcfr]

from @mhalle

The Solutions section text is good, but can be better. I suggest something slightly more introductory like this:

- Each solution represents an application area of 3D Slicer, which may include collection of extensions, 
- tutorials, forum sub-communities, and even custom software distributions tailored to the needs of a 
- specific community. Custom distributions can provide self-contained, end-to-end implementation of 
- specific workflows with simplified user interface.
+ 3D Slicer is designed to be customized and extended to meet the diverse needs of the worldwide 
+ medical and research community. These "3D Slicer solutions" can include extensions to 3D Slicer itself, 
+ specialized tutorials, forum sub-communities, and even custom software distributions designed to 
+ meet specific application needs. For example, solutions can implement specialized functionality, 
+ carefully designed application workflows, or customized user interfaces. 3D Slicer’s open source
+ foundations allow developers to build on the work of others, work across the community, and 
+ contribute back to 3D Slicer’s growing ecosystem.