Fix README.

Fix typo, clarify environment variables.

Change-Id: I87d14e45c7aaf3f5be0aa37ee28b5a4fb70097e8
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/14240
Commit-Queue: Brett Wilson <brettw@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>

README.md

diff --git a/README.md b/README.md
index 2034efb..4bb1a9e 100644
--- a/README.md
+++ b/README.md
@@ -51,7 +51,7 @@
     path. This isn't necessarily the correct trade-off for smaller projects.
 
   * The minimal build configuration is relatively heavyweight. There are several
-    files required and the exact way all compilers are linkers are run must be
+    files required and the exact way all compilers and linkers are run must be
     specified in the configuration (see "Examples" below). There is no default
     compiler configuration.
 
@@ -104,8 +104,8 @@
 similar.
 
 On Linux, Mac and z/OS, the default compiler is `clang++`, a recent version is
-expected to be found in `PATH`. This can be overridden by setting `CC`, `CXX`,
-and `AR`.
+expected to be found in `PATH`. This can be overridden by setting the `CC`, `CXX`,
+and `AR` environment variables.
 
 On z/OS, building GN requires [ZOSLIB](https://github.com/ibmruntimes/zoslib) to be
 installed, as described at that URL. When building with `build/gen.py`, use the option