FAQ: add more details about libgl for end users

Author: jaimergp

docs/maintainer/maintainer_faq.md

@@ -131,7 +131,9 @@ Error:
 ImportError: libGL.so.1: cannot open shared object file: No such file or directory
 ```
 
-To fix the error, create a [yum_requirements.txt](knowledge_base.md#yum-deps) file and add _mesa-libGL_.
+If you saw this error while building a package in your feedstock, create a [yum_requirements.txt](knowledge_base.md#yum-deps) file and add _mesa-libGL_.
+
+If you are seeing this error after installing a package locally, then you are missing an [OpenGL](https://en.wikipedia.org/wiki/OpenGL) provider in your system dependencies. This is more likely to happen in headless systems with no graphics (servers, Docker images, etc). To fix it, you must install a provider like [Mesa](https://www.mesa3d.org/) with your system package manager.
 
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