doc: document that hwloc.xmlfile unsets HWLOC_COMPONENTS

Problem: The documentation of the hwloc.xmlfile job shell option does
not note that its use will also cause HWLOC_COMPONENtS to be unset.

Document this in the submission command man pages as well as
flux-shell(1).

Author: grondo

doc/man1/common/job-shell-options.rst

@@ -38,7 +38,10 @@
        nonzero exit code.
 
    * - :option:`hwloc.xmlfile`
-     - Write hwloc XML gathered by job to a file and set ``HWLOC_XMLFILE``
+     - Write hwloc XML gathered by job to a file and set ``HWLOC_XMLFILE``.
+       Note that this option will also unset ``HWLOC_COMPONENTS`` if set, since
+       presence of this environment variable may cause hwloc to ignore
+       ``HWLOC_XMLFILE``.
 
    * - :option:`output.limit`
      - Set KVS output limit to SIZE bytes, where SIZE may be a floating point

doc/man1/flux-shell.rst

@@ -449,6 +449,8 @@ plugins include:
 .. option:: hwloc.xmlfile
 
   Write the job shell's copy of hwloc XML to a file and set ``HWLOC_XMLFILE``.
+  Note that this option will also unset ``HWLOC_COMPONENTS`` since presence
+  of this environment variable may cause hwloc to ignore ``HWLOC_XMLFILE``.
 
 .. warning::
   The directory referenced by :envvar:`FLUX_JOB_TMPDIR` is cleaned up when the