Fixed a typo in the README

Fixed a trivial typo in the README.

Author: judy2k

README.md

@@ -19,7 +19,7 @@ EOL in April 2021.
 ## Installation
 You can get the release tarball from our [Downloads
 Page](https://www.mongodb.com/try/download/shell). We currently maintain MongoDB
-Shell on three different platofrms - Windows(zip), MacOS(tgz) and Linux(tgz).
+Shell on three different platforms - Windows(zip), MacOS(tgz) and Linux(tgz).
 Once downloaded, you will have to extract the binary and add it to your PATH
 variable. For detailed instructions for each of our supported platforms, please visit
 [installation documentation](https://docs.mongodb.com/mongodb-shell/install#mdb-shell-install)