clarify the docs as to which set types are currently implemented

vlcn-io/cr-sqlite#185

pages/background.mdx

@@ -1,5 +1,3 @@
-import { Callout } from "nextra-theme-docs";
-
 # Background
 
 We want applications:

pages/cr-sqlite/crdts/about.mdx

@@ -4,6 +4,8 @@
 
 The big idea is that you define a table then say which CRDTs should be used to model it.
 
+Notional example (as a [custom syntax for crdts](/cr-sqlite/custom-syntax)):
+
 ```sql
 CREATE CLSet post (
  id INTEGER PRIMARY KEY,
@@ -19,9 +21,9 @@ Tables can be thought of as a set of rows where the identity of each row is its
 
 cr-sqlite supports modeling tables as:
 
-1. Delete Wins Sets
-2. Causal Length Sets
-3. Grow Only Sets
+1. Delete Wins Sets (✅ implemented)
+2. Causal Length Sets (🦺 coming soon)
+3. Grow Only Sets (🦺 coming soon)
 
 See [Table CRDTs](./table-crdts).
 

pages/cr-sqlite/custom-syntax.mdx

@@ -1,8 +1,14 @@
+import { Callout } from "nextra-theme-docs";
+
 # Custom Syntax
 
-A current eye-sore of CR-SQLite is the use of `SELECT` statements to invoke functions which do some sort of modification of the database schema. Another eye-sore is the requirement to wrap alterations of `crr`s with [crsql_begin_alter](/cr-sqlite/api-methods/crsql_begin_alter) and [crsql_commit_alter](/cr-sqlite/api-methods/crsql_commit_alter).
+A current eye-sore of CR-SQLite is the use of `SELECT` statements to invoke functions which do some sort of modification of the database schema. E.g., converting a table to a crdt requires running: `SELECT crsql_as_crr('table_name')`.
+
+Another eye-sore is the requirement to wrap alterations of `crr`s with [crsql_begin_alter](/cr-sqlite/api-methods/crsql_begin_alter) and [crsql_commit_alter](/cr-sqlite/api-methods/crsql_commit_alter).
+
+Luckily, we're partnering with the folks over at the [libsql](https://libsql.org/) project to add a dedicated syntax for CRR creation and modification. 
 
-Luckily, we're partnering with the folks over at the [libsql](https://libsql.org/) project to add a dedicated syntax for CRR creation and modification.
+> Note: we're also converting `crsql_as_crr` to a virtual table to simplify syntax: https://github.com/vlcn-io/cr-sqlite/issues/181
 
 ```sql
 CREATE TABLE post (