Fix typos in README.md

Change-Id: I480ac1a781b09bbbd3e740282ffa1e944da705e9
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/12180
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>

README.md

diff --git a/README.md b/README.md
index 2f5d232..a581eba 100644
--- a/README.md
+++ b/README.md
@@ -188,16 +188,16 @@
 toolchain such as compiler, linker, and build tool. But the large
 centrally controlled projects that GN is designed for typically want a more
 hermetic environment. They will ensure that developers are using a specific
-compatible toolchain that is versioned with the code
+compatible toolchain that is versioned with the code.
 
 As a result, GN expects that the project choose the appropriate version of GN
 that will work with each version of the project. There is no "current stable
 version" of GN that is expected to work for all projects.
 
-As a result, the GN developers to not maintain any packages in any of the
+As a result, the GN developers do not maintain any packages in any of the
 various packaging systems (Debian, RedHat, HomeBrew, etc.). Some of these
 systems to have GN packages, but they are maintained by third parties and you
-should use at your own risk. Instead, we recommend you refer your checkout
+should use them at your own risk. Instead, we recommend you refer your checkout
 tooling to download binaries for a specific hash from [Google's build
 infrastructure](https://chrome-infra-packages.appspot.com/p/gn/gn) or compile
 your own.