Update 2 files

- /assays/plant_phenotyping/protocols/phenotype_at_harvest.txt
- /assays/plant_phenotyping/protocols/phenotype_at_harvest.md

assays/plant_phenotyping/protocols/phenotype_at_harvest.md

+## Phenotype plants at harvest
+
+- scored when plants were fully mature and dry
+- all data was scored on the first emerging shoot (main culm)
+
+**Phenotypic data:**
+- Spike length:  distance from top to bottom grain
+- Floret number: Number of developed florets on the spike (full and empty)
+- Grain number: Number of grains on the spike
+- Fertility: ratio of grains to florets on the spike
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