docs/developer/developer.adoc: added cmake command which enables docs building

Follows the PR #1169.

Author: matusmarhefka

docs/developer/developer.adoc

@@ -92,7 +92,8 @@ To install Doxygen, you can run `dnf install doxygen`.
 Run the following command to build the documentation:
 
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-make docs
+$ cmake -DENABLE_DOCS=TRUE ../
+$ make docs
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 The resulting documentation is located in `build/docs` directory in these