added plantUML exercise

plantuml/gilded-rose.puml

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+@startuml
+
+start
+note left
+    Do this for each item in the list.
+    An item has a name, a sell in value and a quality value
+end note
+
+if (not "Aged Brie" and not "Backstage passes to a TAFKAL80ETC concert") then (yes)
+    if (quality > 0) then (yes)
+        if (not "Sulfuras, Hand of Ragnaros") then (yes)
+            -lower quality with 1
+        endif
+    endif
+else (no)
+    if (quality < 50) then (yes)
+        -increase quality with 1
+        if ("Backstage passes to a TAFKAL80ETC concert") then (yes)
+            if (sell in < 11) then (yes)
+                if (quality < 50) then (yes)
+                    -increase quality with 1
+                endif
+            endif
+            if (sell in < 6) then (yes)
+                if (quality < 50) then (yes)
+                    -increase quality with 1
+                endif
+            endif
+        endif
+    endif
+endif
+
+if (not "Sulfuras, Hand of Ragnaros") then (yes)
+    -lower quality with 1
+endif
+
+if (sell in < 0) then (yes)
+    if (not "Aged Brie") then (yes)
+        if (not "Backstage passes to a TAFKAL80ETC concert") then (yes)
+            if (quality > 0) then (yes)
+                if (not "Sulfuras, Hand of Ragnaros") then (yes)
+                    -lower quality with 1
+                endif
+            endif
+        else (no)
+            -lower quality with quality
+        endif
+    else (no)
+        if (quality < 50) then (yes)
+            -increase quality with 1
+        endif
+    endif
+endif
+
+stop
+
+@enduml

plantuml/readme.md

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+# PlantUML
+This UML refactoring exercise is aimed at less technical people like analysts, testsers and other non-programmers. The key takeaway message is clarifying the need for continuous refactoring to people who do not code on a daily basis.
+
+## Running and rendering
+Several alternatives are available to render PlantUML, see https://plantuml.com/running.
+
+## Syntax
+For the syntax of activity diagrams in PlantUML, please refer to https://plantuml.com/activity-diagram-beta
+
+# Exercise
+You can find the original GildedRose challenge in the gilded-rose.puml file.
+
+If you want to illustrate how this activity diagram got to this state, you can show the requirements and the files under the /history directory. These individual files show the evolution of the activity diagram.