add note on QC in data prep
@@ -26,6 +26,8 @@ Note that "strain" here carries no biological or functional significance and sho
The sequence itself is a **[consensus genome](https://en.wikipedia.org/wiki/Consensus_sequence#:~:text=In%20molecular%20biology%20and%20bioinformatics,position%20in%20a%20sequence%20alignment.)**.
**By default, sequences less than 27,000 bases in length or with more than 3,000 `N` (unknown) bases are omitted from the analysis.**
+For a basic QC and preliminary analysis of your sequence data, you can use [clades.nextstrain.org](https://clades.nextstrain.org/).
+This tool will check your sequences for excess divergence, clustered differences from the reference, and missing or ambiguous data. In addition, it will assign nextstrain clades and call mutations relative to the reference.
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