Defined period for stress frame

See bird-sanctuary/bluejay#216

README.md

@@ -86,7 +86,7 @@ This is where EDT versions come into play if not explicitly stated, the values a
 - `011 0 mmmm mmmm` - **Current** frame with a step size of 1A [0, 1, ..., 255]
 - `100 0 mmmm mmmm` - **Debug frame 1** not associated with any specific value, can be used to debug ESC firmware
 - `101 0 mmmm mmmm` - **Debug frame 2** not associated with any specific value, can be used to debug ESC firmware
-- `110 0 mmmm mmmm` - **Stress level** frame [0, 1, ..., 255] (since v2.0.0)
+- `110 0 mmmm mmmm` - **Stress level** frame [0, 1, ..., 255] (since v2.0.0) since last stress level frame (defined in v2.1.2)
 - `111 0 mmmm mmmm` - **Status frame**: Bit[7] = alert event, Bit[6] = warning event, Bit[5] = error event, Bit[3-0] - Max. stress level [0-15] (since v2.0.0). At this moment Bit[4] is not being used.
 
 ### Checksum
@@ -140,6 +140,7 @@ A bi-directional response frame (EDT frame) is to be sent 30μs after a DSHOT fr
 * [DSHOT - The missing Handbook](https://brushlesswhoop.com/dshot-and-bidirectional-dshot/)
 
 ## History
+* v2.1.2 - Defined period for stress level frame
 * v2.1.1 - Clarified Bit index direction
 * v2.1.0 - Added section about timing
 * v2.0.2 - Fixed typo in stress level frame