tweak readme

Author: samuelcolvin

README.rst

@@ -13,8 +13,8 @@ pydf easier to use, in particular this means pydf works on heroku.
 Currently using **wkhtmltopdf 0.12.5 for Ubuntu 18.04 (bionic)**, requires **Python 3.6+**.
 
 **If you're not on Linux amd64:** pydf comes bundled with a wkhtmltopdf binary which will only work on Linux amd64
-architectures. If you're on another OS or architecture your milage may vary, it is likely that you'll need to supply
-your own wkhtmltopdf binary and point pydf towards it by setting the ``WKHTMLTOPDF_PATH`` variable.
+architectures. If you're on another OS or architecture your mileage may vary, it is likely that you'll need to supply
+your own wkhtmltopdf binary and point pydf towards it by setting the ``WKHTMLTOPDF_PATH`` environment variable.
 
 Install
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