Update README.md

Author: derobins

README.md

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 HDF5 Compression Plugins
+------------------------
 
 *Please refer to the Building.txt file for installation instructions.*
 
@@ -7,6 +8,22 @@ HDF5® data model API. The HDF5® data model has been adopted across
 many industries and this implementation has become a de facto data management standard
 in science, engineering, and research communities worldwide.
 
+Compression plugins are divided into two categories:
+
+1) Maintained
+
+These filters get their own directory off the root, are actively maintained,
+and are deployed with the HDF5 library when we create a release.
+
+2) Community
+
+These are located in the `community` directory and may not be actively maintained.
+This directory is instead intended to be a one-stop-shopping location for information about
+filters found in the wild, with links to code and maintainers. The hope is that, even
+if the filters become unmaintained, enough information can be found here to decode
+the data in the file, even if that would require more effort, such as having to
+adapt code that hasn't been maintained in a long time.
+
 The HDF Group is the developer, maintainer, and steward of HDF5 software. Find more
 information about The HDF Group, the HDF5 Community, and other HDF5 software projects,
 tools, and services at [The HDF Group's website](https://www.hdfgroup.org/).