Fixed a typo (#57)

zilsd.adoc

@@ -34,7 +34,7 @@ The Zilsd extension adds the following RV32-only instructions:
 |===
 
 As the access size is 64-bit, accesses are only considered naturally aligned for effective addresses that are a multiple of 8.
-In this case, these instruction are guaranteed to not raise an address-misaligned exception.
+In this case, these instructions are guaranteed to not raise an address-misaligned exception.
 Even if naturally aligned, the memory access might not be performed atomically.
 
 If the effective address is a multiple of 4, then each word access is required to be performed atomically.