README: Reflect recent changes to the Xcode framework setup

[DivineDominion]

The "Copy Files" phase doesn't exist anymore, and I added a note about framework lookup.

Closes #199

[fletcher]

README.md is generated via CMake in order to include up to date versioning, etc. To make changes, you have to modify the template file instead.

I'll need to review, since I now use Cmake directly to include libMultiMarkdown in other projects, rather than dragging the xcodeproj file indirectly.

[DivineDominion]

At least step 5 can safely be removed from the source; see

There's no "Copy Files" build phase anymore.

[DivineDominion]

Just tested with a fresh Xcode project; all of the steps I mention are still necessary to get libMMD running in Xcode with ObjC