Actually microHAL is in strong development so ther is no stable documentation, when first version will be relisted documentation will be available under this link. Now only way to get documentation is to generate itself.
Firstly click on blue 'at' symbol on your microIDE.
After clicking on this button a new window should appear. In new window you should find microHAL project and expand it. Inside should be HAL-DOC.doxyfile please select it and click OK.
Now documentation will be generated, this can take some time. After entire generation process in microHAL project you should see html directory (if you can't see this directory please refresh project by pressing F5 key). Inside the folder should be index.html with is start point of documentation.