Merge ~xavpaice/charm-nrpe:update_docs into charm-nrpe:master

[Xav Paice]

update docs for nagios_master config

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PASSED: Continuous integration, rev:709c62656d7bfa0d4e05b69323d193e2aaa2a069
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review: Approve (continuous-integration)

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Change successfully merged at revision 358b563672cf7b51f9f0f78ec46c4d146b5093d9

diff --git a/config.yaml b/config.yaml
index 4494993..68bcd03 100644
--- a/config.yaml
+++ b/config.yaml
@@ -3,7 +3,10 @@ options:
     default: "None"
     type: string
     description: |
-        IP address of the nagios master from which to allow rsync access
+        IP address of the nagios master from which to allow NRPE access, and/or
+        rsync if export_nagios_definitions is set to True.  This setting allows
+        the Nagios servers listed to connect to NRPE in addition to any added
+        by relation data.
   server_port:
     default: 5666
     type: int