some tutorial updates

Author: nsheff

docs/decision_record.md

@@ -541,7 +541,7 @@ The POST body for the local comparison is a "level 2" sequence collection, like
 
 ### Rationale
 
-We wanted to stick with the REST guideline of noun endpoints with GET that describe what you are retrieving. As recommended in the [service-info specification](https://github.com/ga4gh-discovery/ga4gh-service-info#how-do-i-describe-a-service-implementing-multiple-specifications), a prefix, like `/seqcol/...` could be added by a service that implemented multiple specifications, but this kind of namespace it outside the scope of the specification itself. We considered doing `/{digest1}/compare/{digest2}` and that would have been fine. In the end we liked the symmetry of `/comparison` and `/collection` as parallel endpoints. For the retrieval endpoint we considered `/secol` or `/sequence-collection` or `/seqCol`, but wanted to keep structure parallel to the refget `/sequence` endpoint.
+We wanted to stick with the REST guideline of noun endpoints with GET that describe what you are retrieving. As recommended in the [service-info specification](https://github.com/ga4gh-discovery/ga4gh-service-info#how-do-i-describe-a-service-implementing-multiple-specifications), a prefix, like `/seqcol/...` could be added by a service that implemented multiple specifications, but this kind of namespace it outside the scope of the specification itself. We considered doing `/{digest1}/compare/{digest2}` and that would have been fine. In the end we liked the symmetry of `/comparison` and `/collection` as parallel endpoints. For the retrieval endpoint we considered `/seqcol` or `/sequence-collection` or `/seqCol`, but wanted to keep structure parallel to the refget `/sequence` endpoint.
 
 ### Limitations
 

docs/digest_from_fasta.md

@@ -1,7 +1,32 @@
 
-# Digest from fasta
+# Compute a seqcol digest given a sequence collection
 
-One of the most common uses of the seqcol specification is to compute a standard, universal identifier from a FASTA file.
+One of the most common uses of the seqcol specification is to compute a standard, universal identifier for a particular sequence collection. There are two ways to approach this: 1. Using an existing implementation; 2. Implement the seqcol digest algorithm yourself (it's not that hard).
 
-We are working on defining the final algorithm. This page is a placeholder for once the algorithm is defined.
+## 1. Using existing implementations
+
+### Reference implementation in Python
+
+If working from within Python, you can use the reference implementation like this:
+
+1. Install the seqcol package with some variant of `pip install seqcol`.
+2. Build up your canonical seqcol object
+3. Compute its digest:
+
+```
+seqcol.digest(seqcol_obj)
+```
+
+
+
+#### From a Canonical Sequence Collection
+
+If you have a sequence collection in canonical structure, you can get its digest like this:
+
+
+
+```
+import seqcol
+
+seqcol.digest()