remove duplicated text

Signed-off-by: Michael Friis <friism@gmail.com>

docs/reference/run.md

@@ -1445,7 +1445,7 @@ The `host-src` can either be an absolute path or a `name` value. If you
 supply an absolute path for the `host-dir`, Docker bind-mounts to the path
 you specify. If you supply a `name`, Docker creates a named volume by that `name`.
 
-A `name` value must start with start with an alphanumeric character,
+A `name` value must start with an alphanumeric character,
 followed by `a-z0-9`, `_` (underscore), `.` (period) or `-` (hyphen).
 An absolute path starts with a `/` (forward slash).