[readme] add explanation for opiate

README.md

@@ -66,6 +66,7 @@ the following is the current list of plugins
 - `reverter`: play sound backwards
 - `panera`: pan individual notes differently
 - `velociter`: random velocity setter
+- `opiate`: spectral morphing between two audio signals
 
 there's a bit of an explanation of each of the plugins below, but it's not a thorough documentation or a manual, it's just a bunch of notes i've written and a short description of the parameters
 
@@ -298,6 +299,15 @@ params:
 
 it'll set the velocity of every incoming midi note to be in the range `[min_vel, max_vel)`
 
+### opiate
+
+opiate is a spectral morphing plugin. you have to provide it 4 input channels (two stereo signals), and it'll do spectral morphing between the two
+
+params:
+- `morph`: how much to morph from audio 1 to 2
+
+if `morph` is set to 0, only audio 1 will play. if it's set to 1, only audio 2 will play. values in between will morph between the two audio signals
+
 ## contributing
 
 issues and prs are welcome, but please open an issue before making any big pr, i don't wanna have to reject a pr where you have put a lot of effort on. if you are fine with that, ig go ahead i'm not your mum