add mermaid overview

arc-mermaid.md

+```mermaid
+flowchart TD
+    Maleckova-2019-Talinum-ABA[Maleckova-2019-Talinum-ABA]
+    Maleckova-2019-Talinum-ABA-->STUDY_Maleckova2018_aba
+    subgraph STUDY_Maleckova2018_aba[Study:Maleckova2018_aba]
+        plant_material[plant_material]
+        treatment_harvest[treatment_harvest]
+    end
+    subgraph ASSAY_CMML_18-0008_LCqTOF[Assay:CMML_18-0008_LCqTOF]
+        metabolite_extraction[metabolite_extraction]
+        liquid_chromatography[liquid_chromatography]
+    end
+    subgraph ASSAY_CMML_18-0008_GC-MS[Assay:CMML_18-0008_GC-MS]
+        metabolite_extraction[metabolite_extraction]
+        gas_chromatography[gas_chromatography]
+        mass_spectrometry[mass_spectrometry]
+    end
+    subgraph ASSAY_Maleckova2018_aba_mRNASeq[Assay:Maleckova2018_aba_mRNASeq]
+        RNAex[RNAex]
+        Illumina[Illumina]
+    end
+    subgraph ASSAY_CMML_18-0008_LCqTOF-MasshunterQuant[Assay:CMML_18-0008_LCqTOF-MasshunterQuant]
+    end
+    subgraph ASSAY_CMML_18-0008_GC-MS-MasshunterQuant[Assay:CMML_18-0008_GC-MS-MasshunterQuant]
+    end
+    subgraph ASSAY_CMML_18-0008_HPLC-DAD[Assay:CMML_18-0008_HPLC-DAD]
+    end
+    plant_material-->|24|treatment_harvest
+    treatment_harvest-->|24|metabolite_extraction
+    treatment_harvest-->|24|metabolite_extraction_1
+    treatment_harvest-->|24|RNAex
+    metabolite_extraction-->|48|liquid_chromatography
+    metabolite_extraction_1-->|48|gas_chromatography
+    gas_chromatography-->|63|mass_spectrometry
+    RNAex-->|24|Illumina
+
+classDef inv fill:#6c7885,color:#2d3e50,font-weight:bold;
+classDef study fill:#62d4c1,color:#2d3e50,font-weight:bold;
+classDef assay fill:#ffd34d,color:#2d3e50,font-weight:bold;
+classDef process fill:#D46275,color:#2d3e50,font-weight:;
+class Maleckova-2019-Talinum-ABA inv;
+class STUDY_Maleckova2018_aba study;
+class ASSAY_CMML_18-0008_LCqTOF,ASSAY_CMML_18-0008_GC-MS,ASSAY_Maleckova2018_aba_mRNASeq,ASSAY_CMML_18-0008_LCqTOF-MasshunterQuant,ASSAY_CMML_18-0008_GC-MS-MasshunterQuant,ASSAY_CMML_18-0008_HPLC-DAD assay;
+class plant_material,treatment_harvest,metabolite_extraction,liquid_chromatography,metabolite_extraction_1,gas_chromatography,mass_spectrometry,RNAex,Illumina process;
+```