Merge pull request #24 from orthographic-pedant/spell_check/across

Fixed typographical error, changed accross to across in README.

README.md

@@ -14,7 +14,7 @@ Features
 * `Non-intrusive.` pam\_usb doesn't require any modifications of the USB storage device to work (no additional partitions required).
 * USB Serial number, model and vendor verification.
 * Support for **One Time Pads** authentication.
-* You can use the same device accross multiple machines.
+* You can use the same device across multiple machines.
 * Support for all kind of removable devices (SD, MMC, etc).
 
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