add snapshot~ to known limitation docs

docs/02.getting_started.md

@@ -104,5 +104,6 @@ This list will be continuously epanded to document differences in object behavio
 * On the `[select]` object it is currently not possible to set the arguments via the right inlet (internally a hardcoded switch_case is used).
 * Heavy supports remote/send messages, however empty messages are currently removed. So the typical `[; bla 1(` multiline message needs to contain at least something on the first line: `[_; bla 1(`.
 * `[metro]` and `[timer]` objects do not accept tempo messages or unit arguments.
+* `[snapshot~]` does not respond within the same control flow as it executes in signal context. Its output happens on the next audio cycle, so additional care for this control flow needs to be taken into account if you depend on synchronous execution.
 * Certain filters are sensitive to ‘blowing up’ at very low or very high cutoff frequencies and/or resonances, due to the filter coefficients not being perfectly represented with a finite number of bits. While Pure data natively uses 64 bits, platforms like `OWL` and `Daisy`  that use 32 bit float are more sensitive to this. For example, the Pure data `[lp~]`, `[bp~]` and `[hp~]` filters are implemented with biquads which are prone to fail or distort with cutoff frequencies less than around 200 Hz (at 48kHz sample rate).
 * Heavy does not support multichannel connections.