v0.3: updated README.md

This is third development version of program. Below are changes since last release:

Added

• Better info about lack of layout file
• Better info about errors in templates files
• Server monitor changes in layout files too
• Composite tags

Changed

• Updated README.md
• Regenerate only needed files not whole site

Fixed

• Server crash on missing file during site generation
• Server crash on error in template file
• Crash on comment in markdown file