Add parameter example plugin

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diff --git a/plugins/eg-params.lv2/README.txt b/plugins/eg-params.lv2/README.txt
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+== Params ==
+
+The basic LV2 mechanism for controls is
+http://lv2plug.in/ns/lv2core#ControlPort[lv2:ControlPort], inherited from
+LADSPA.  Control ports are problematic because they are not sample accurate,
+support only one type (`float`), and require that plugins poll to know when a
+control has changed.
+
+Parameters can be used instead to address these issues.  Parameters can be
+thought of as properties of a plugin instance; they are identified by URI and
+have a value of any type.  This deliberately meshes with the concept of plugin
+state defined by the http://lv2plug.in/ns/ext/state[LV2 state extension].
+The state extension allows plugins to save and restore their parameters (along
+with other internal state information, if necessary).
+
+Parameters are accessed and manipulated using messages sent via a sequence
+port.  The http://lv2plug.in/ns/ext/patch[LV2 patch extension] defines the
+standard messages for working with parameters.  Typically, only two are used
+for simple plugins: http://lv2plug.in/ns/ext/patch#Set[patch:Set] sets a
+parameter to some value, and http://lv2plug.in/ns/ext/patch#Get[patch:Get]
+requests that the plugin send a description of its parameters.