Add Genesis Slot to timestamp-slot conversion

tips/TIP-0046/tip-0046.md

@@ -67,14 +67,14 @@ slots and each slot is `Slot Duration In Seconds` seconds in length.
 ### Slot Index
 
 Each slot has a corresponding slot index, which is a `uint32`. To calculate the slot index of a timestamp, the protocol
-parameters `Genesis Unix Timestamp` and `Slot Duration In Seconds` are used. The slot index of a Unix timestamp
-`Unix Timestamp` (in seconds) is calculated as follows:
+parameters `Genesis Slot`, `Genesis Unix Timestamp` and `Slot Duration In Seconds` are used. The slot index of a Unix
+timestamp `Unix Timestamp` (in seconds) is calculated as follows:
 
 - Compute `Elapsed Time` as `Unix Timestamp - Genesis Unix Timestamp`.
-- If `Elapsed Time < 0`, the slot index is `0`.
-- Otherwise the slot index is `Elapsed Time/Slot Duration In Seconds + 1`.
-  - Note: The `+ 1` is required because slots are counted starting from `1` with `0` being reserved for times before the
-    genesis, which has to be addressable as its own slot.
+- If `Elapsed Time < 0`, the slot index is `Genesis Slot`.
+- Otherwise the slot index is `Genesis Slot + Elapsed Time/Slot Duration In Seconds + 1`.
+  - Note: The `+ 1` is required because slots are counted starting from `1`. `0` is reserved for times before the
+    genesis (if `Genesis Slot = 0`), which has to be addressable as its own slot.
 
 ### Epoch Index