The documentation is like you say really scarce.
The best I found is to download the latest source code here : https://github.com/loresoft/msbuildtasks
The latest documentation can also be viewed via GitHub directly without downloading the source: https://github.com/loresoft/msbuildtasks/tree/master/Documentation
If installed using the MSI, you can also look at the XSD found in the installation folder (C:\Program Files (x86)\MSBuild\MSBuildCommunityTasks\MSBuild.Community.Tasks.xsd) to at least see which tasks are avaialable to you and the documentation connected with them.