emphasize no special characters in indices allowed #61

Author: sreichl

config/README.md

@@ -6,7 +6,7 @@ You need one configuration file to configure the analyses and one annotation fil
 - sample annotation (annotation): CSV file consisting of four mandatory columns.
     -  name: A unique name for the dataset (tip: keep it short but descriptive).
     -  data: Path to the tabular data as a comma-separated table (CSV).
-    -  metadata: Path to the metadata as a comma-separated table (CSV) with the first column being the index/identifier of each observation/sample and every other column metadata for the respective observation (either numeric or categorical, not mixed). **No NaN or empty values allowed.**
+    -  metadata: Path to the metadata as a comma-separated table (CSV) with the first column being the index/identifier of each observation/sample and every other column metadata for the respective observation (either numeric or categorical, not mixed). **No NaN or empty values allowed, and no special characters (all except a-z, 0-9, `_`) in the index.**
     -  samples_by_features: Boolean indicator if the data matrix is observations/samples (rows) x features (columns): 0==no, 1==yes.
 
-Set workflow-specific `resources` or command line arguments (CLI) in the workflow profile `workflow/profiles/default.config.yaml`, which supersedes global Snakemake profiles.
+Set workflow-specific `resources` or command line arguments (CLI) in the workflow profile `workflow/profiles/default.config.yaml`, which supersedes global Snakemake profiles.