Correct typo in README.md

Author: RobertRostohar

CMSIS/Documentation/README.md

@@ -2,7 +2,7 @@
 
 CMSIS 6 Documentation in HTML format is published online at [https://arm-software.github.io/CMSIS_6](https://arm-software.github.io/CMSIS_6).
 
-The version drop-down menu in the "Overview" book allows to switch between the documentation provided with offical releases and the latest draft documentation for the main branch.
+The version drop-down menu in the "Overview" book allows to switch between the documentation provided with official releases and the latest draft documentation for the main branch.
 
 The documentation source is maintained in `/CMSIS/Documentation/Doxygen/` folder as a mixture of markdown and doxygen formats. Software source and header files, templates and examples may also contribute information that gets integrated into the final documentation.