tree_structure_view.md: fix link to plugin.xml on GH
tree_structure_view.md: fix link to plugin.xml on GH

artspb/intellij-sdk-docs,JetBrains/intellij-sdk-docs,JetBrains/intellij-sdk-docs,JetBrains/intellij-sdk-docs,artspb/intellij-sdk-docs,artspb/intellij-sdk-docs,artspb/intellij-sdk-docs