added readme

README.md

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+# Tuba synthesizer
+
+If you are interested, leave an issue at 
+[project home](https://gitea.sergeych.net/SergeychWorks/karabass).
+
+
+This is proof-of-concept synthesizer of the tuba musical instrument. It synthesizes
+the sound from characteristical overtones, not from real instrument samples or FM synthesis.
+It also uses more or less proper envelope and more effects to make it recognizable.
+
+Current limitations:
+
+- slow response, like real tube, it gets some time to produce sound and hardly can play short notes.