Fix documentation for "pool" object in gn binary.

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 2133 matching lines @@
 
 ```
 ## **pool**: Defines a pool object.
 
 ```
   Pool objects can be applied to a tool to limit the parallelism of the
   build. This object has a single property "depth" corresponding to
   the number of tasks that may run simultaneously.
 
   As the file containing the pool definition may be executed in the
-  of more than one toolchain it is recommended to specify an explicit
-  toolchain when definining and referencing a pool.
+  context of more than one toolchain it is recommended to specify an
+  explicit toolchain when defining and referencing a pool.
 
   A pool is referenced by its label just like a target.
 
 ```
 
 ### **Variables**
 
 ```
   depth*
   * = required
@@ skipping 3925 matching lines @@
 **  \--root**: Explicitly specify source root.
 **  \--runtime-deps-list-file**: Save runtime dependencies for targets in file.
 **  \--script-executable**: Set the executable used to execute scripts.
 **  \--threads**: Specify number of worker threads.
 **  \--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.
 
 ```