Fix typo

README.md

@@ -67,7 +67,7 @@ targets to build Proton:
 You may need to restart the Steam client to see it. The tool's name in the
 Steam client will be based on the currently checked out branch of Proton. You
 can override this name using the `build_name` make variable, which can be set 
-via an evironment variable or an argument to the make command 
+via an environment variable or an argument to the make command 
 [among other ways](https://www.gnu.org/software/make/manual/html_node/Values.html#Values).
 
 `make redist` - This will create a build which you can easily redistribute to