Documentation: Add a note on no length restrictions for plugin output/perfdata.

Fixes #6452

doc/1-about.md

@@ -107,6 +107,7 @@ runtime evaluated macros.
 Three types of commands used for different actions: checks, notifications and events.
 Check timeout for commands instead of a global option. Commands also have custom attributes allowing
 you to specify default values.
+There is no plugin output or performance data length restriction anymore compared to Icinga 1.x.
 
 * Custom Runtime Macros
 

doc/5-addons-plugins.md

@@ -54,3 +54,6 @@ Currently Icinga 2 supports the native plugin API specification from the `Monito
 project.
 
 The `Monitoring Plugin API` is defined in the [Monitoring Plugins Development Guidelines](https://www.monitoring-plugins.org/doc/guidelines.html).
+
+There are no output length restrictions using Icinga 2. This is different to the
+[Icinga 1.x plugin api definition](http://docs.icinga.org/latest/en/pluginapi.html#outputlengthrestrictions).

doc/8-migration.md

@@ -1177,6 +1177,9 @@ Icinga 2 does not make a difference between `output` (first line) and
 `long_output` (remaining lines) like in Icinga 1.x. Performance Data is
 provided separately.
 
+There is no output length restriction as known from Icinga 1.x using an
+[8KB static buffer](http://docs.icinga.org/latest/en/pluginapi.html#outputlengthrestrictions).
+
 The `StatusDataWriter`, `IdoMysqlConnection` and `LivestatusListener` types
 split the raw output into `output` (first line) and `long_output` (remaining
 lines) for compatibility reasons.