Fix circular link in guidelines.md

Point link to detailed licensing page instead of to itself, to resolve issue #946

Author: Amanda Butler

docs/reference/contributing/guidelines/guidelines.md

@@ -30,7 +30,7 @@ Most Mbed OS software is licensed under a permissive license. The three most
 
 For new Mbed projects, we suggest adopting the Apache 2.0 license. Note that any Mbed software release under a permissive license cannot accept any code that is licensed under a "copyleft" license. Doing so would prevent us from continuing to distribute our code under the permissive license. You are welcome to use Mbed software with copyleft licenses, as long as the rules of the copyleft license are followed.
 
-You can find a more detailed description on licenses in the [contributing guidelines](../contributing/index.html#licensing).
+You can find a more detailed description on licenses in the [contributing guidelines](../contributing/license.html).
 
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