update readme with link to subject

README.md

 # Synthe
 
+Lab instructions: [https://mee-labs.gitlab-pages.imt-atlantique.fr/vhdl/synthe/](https://mee-labs.gitlab-pages.imt-atlantique.fr/vhdl/synthe/)
+
 ## Description
 Project to build a digital synthesizer in VHDL.
 4 types of waveform can be played: sine, square, triangle, saw-tooth.