add note about macOS share and exec policy

fix whitespaces

stdlib/Mmap/src/Mmap.jl

@@ -166,6 +166,10 @@ will be visible to other processes mapping the same file.
 
 The `exec` keyword argument specifies whether the underlying mmap data will be executable.
 
+!!! note
+    On MacOS `exec=true` implies `shared=false`, because each thread has its own access permissions to `mmap` regions.
+
+
 For example, the following code
 
 ```julia
@@ -220,12 +224,12 @@ function _mmap(io::IO,
     if exec && !iswritable(io)
         throw(ArgumentError("$io must be writeable to mmap with exec = true"))
     end
-   @static if Sys.isapple()
-      # on MacOS each thread has its own access permissions, so we can't share when exec=true
-      # https://developer.apple.com/documentation/apple-silicon/porting-just-in-time-compilers-to-apple-silicon#Disable-Write-Protections-Before-You-Generate-Instructions
-      exec && (shared = false)
-   end
-   
+    @static if Sys.isapple()
+       # on MacOS each thread has its own access permissions, so we can't share when exec=true
+       # https://developer.apple.com/documentation/apple-silicon/porting-just-in-time-compilers-to-apple-silicon#Disable-Write-Protections-Before-You-Generate-Instructions
+       exec && (shared = false)
+    end
+
     len = sizeof(T)
     for l in dims
         len, overflow = Base.Checked.mul_with_overflow(promote(len, l)...)