[README.md] rendering problem because of a missing new line

After last addition of a target, a new line was missing and that's why
there was a redering problem with a header line (Supported Toolchains
and IDEs).
[README.md] corrected the toolchains for IDEs CoIDE and emBlocks
Merge pull request #553 from ohagendorf/master

README - rendering problem because of a missing new line