Update README.md

Minor update to have comment prepended. I just uncommented it and the error was slightly non-obvious.

README.md

@@ -29,7 +29,7 @@
     end,
     -- ft = { 'tex', 'bib' }, -- Lazy-load on filetype
     build = 'go build'
-    -- build = 'go build -o ~/.bin/' if e.g. ~/.bin/ is in $PATH
+    -- build = 'go build -o ~/.bin/' -- if e.g. ~/.bin/ is in $PATH
 }
 ```