Update SA1011 documentation for function pointers

Author: sharwell

documentation/SA1011.md

@@ -34,6 +34,7 @@ A closing square bracket should be followed by whitespace unless:
 * It is followed by certain types of operator symbols
 * It is followed by a nullable reference type annotation for arrays (for example, `string[]? items`)
 * It is followed by the null-forgiving operator applied to an array or element access (for example, `values[0]!`)
+* It is immediately followed by a `<` in an unmanaged calling convention list for a function pointer, for example `delegate* unmanaged[Cdecl]<void>`
 
 ## How to fix violations