Update about.rst

One grammar tweak and one typo fix.  Nitpicky, but since they are at the start of the first page of the docs, and first impressions are so important...
Merge pull request #449 from ellerychan/patch-1

Update about.rst
Add CMakeModules for SilverLining and Triton
Merge branch 'master' of github.com:gwaldron/osgearth
Add the Triton ocean plugin.
add ocean API call
Add missing SL class
Triton
merge with master
Triton and compile fixes
spelling grammar
Update simple ocean
Clean up simple ocean dir
rename ocean_surface to ocean_simple
simple ocean compile fix
Merge pull request #450 from dfries/patch-1

spelling grammar
make SL and Triton work together (with lighting)
Merge branch 'master' of github.com:gwaldron/osgearth
Fixed issue with picking sometimes failing on projected maps.
Merge branch 'master' of https://github.com/gwaldron/osgearth