Add links to demos for other novoda open source projects

[friedger]

The global readme should contain links to

• https://github.com/novoda/download-manager
• https://github.com/novoda/rxpresso
• https://github.com/novoda/landing-strip
• https://github.com/novoda/rxmocks
• https://github.com/novoda/material-painter
• https://github.com/novoda/merlin
• https://github.com/novoda/simple-easy-xml-parser

[friedger]

fixed by https://github.com/novoda/android-demos/pull/15