gn help switches doc fixup

tools/gn/docs/reference.md

 # GN Reference
 
 *This page is automatically generated from* `gn help --markdown all`.
 
 ## **\--args**: Specifies build arguments overrides.
 
 ```
   See "gn help buildargs" for an overview of how build arguments work.
 
   Most operations take a build directory. The build arguments are taken
@@ skipping 509 matching lines @@
   gn gen <out_dir>
 
   Generates ninja files from the current tree and puts them in the given
   output directory.
 
   The output directory can be a source-repo-absolute path name such as:
       //out/foo
   Or it can be a directory relative to the current directory such as:
       out/foo
 
-  See "gn help" for the common command-line switches.
+  See "gn help switches" for the common command-line switches.
 
 
 ```
 ## **gn help <anything>**
 ```
   Yo dawg, I heard you like help on your help so I put help on the help
   in the help.
 
 
 ```
@@ skipping 4283 matching lines @@
 **  \--nocolor**: Force non-colored output.
 **  -q**: Quiet mode. Don't print output on success.
 **  \--root**: Explicitly specify source root.
 **  \--runtime-deps-list-file**: Save runtime dependencies for targets in file.
 **  \--time**: Outputs a summary of how long everything took.
 **  \--tracelog**: Writes a Chrome-compatible trace log to the given file.
 **  -v**: Verbose logging.
 **  \--version**: Prints the GN version number and exits.
 
 ```