add mermaid graph

arc-mermaid.md

+```mermaid
+flowchart TD
+    classDef investigationStyle fill:#6c7885,color:#2d3e50,fontWeight:bold;
+    classDef studyStyle fill:#62d4c1,color:#2d3e50,fontWeight:bold;
+    classDef assayStyle fill:#ffd34d,color:#2d3e50,fontWeight:bold;
+    classDef processStyle fill:#D46275,color:#2d3e50;
+    id_0["Predmoter—cross-species prediction of {plant} promoter and enhancer regions"]
+    class id_0 investigationStyle;
+    id_0-->STUDY_id_1
+    class STUDY_id_1 studyStyle;
+    subgraph STUDY_id_1[Study: ArchitectureAndProposedModels]
+        id_2[ProposedModels]
+        class id_2 processStyle;
+    end
+    id_0-->STUDY_id_3
+    class STUDY_id_3 studyStyle;
+    subgraph STUDY_id_3[Study: Data]
+        id_4[Preprocessing]
+        class id_4 processStyle;
+        id_5[Filtering]
+        class id_5 processStyle;
+    end
+    subgraph ASSAY_id_6[Assay: Metrics]
+        id_6[Metrics]
+        class id_6 processStyle;
+    end
+    class ASSAY_id_6 assayStyle;
+    subgraph ASSAY_id_7[Assay: PeakCalling]
+        id_7[PeakCalling]
+        class id_7 processStyle;
+    end
+    class ASSAY_id_7 assayStyle;
+    subgraph ASSAY_id_8[Assay: SpeciesSelection]
+        id_9[Cross-speciesPrediction]
+        class id_9 processStyle;
+        id_10[Intra-speciesAndCross-validatio]
+        class id_10 processStyle;
+    end
+    class ASSAY_id_8 assayStyle;
+    id_2-->|10|id_9
+    id_4-->|1|id_5
+    id_7-->|12|id_6
+    id_9-->|10|id_7
+    id_10-->|2|id_7
+
+```