add db config docs and basic schema docs

doc/SUMMARY.md

@@ -8,7 +8,7 @@
 - [CRDTs](crdts.md)
 - [Encryption]()
 - [Gossip]()
-- [Schema]()
+- [Schema](schema.md)
 - [Subscriptions]()
 - [Synchronization]()
 - [Templates]()
@@ -30,7 +30,7 @@
     - [template]()
     - [tls](cli/tls.md)
 - [Configuration](config/README.md)
-    - [db]()
+    - [db](config/db.md)
     - [gossip](config/gossip.md)
     - [api]()
     - [admin]()

doc/config/db.md

@@ -0,0 +1,27 @@
+# The `[db]` configuration
+
+The `[db]` block configures the Corrosion's SQLite database.
+
+### Required fields
+
+#### `db.path`
+
+Path of the sqlite3 database.
+
+```toml
+[db]
+path = "/var/lib/corrosion/db.sqlite"
+```
+
+### Optional fields
+
+#### `db.schema_paths`
+
+Array of paths where [schema]() .sql files are present.
+
+```toml
+[db]
+schema_paths = ["/etc/corrosion/schema", "/path/to/table_name.sql"]
+```
+
+If a directory is specified, all .sql files will be loaded.

doc/schema.md

@@ -0,0 +1,29 @@
+# Schema
+
+Corrosion's schema definition happens via files each representing one or more tables, written in SQL (SQLite-flavored). This is done through `CREATE TABLE` and `CREATE INDEX` exclusively!
+
+Manual migrations are not supported (yet). When schema files change, Corrosion can be reloaded (or restarted) and it will compute a diff between the old and new schema and make the changes.
+
+Any destructive actions on the table schemas are ignored / prohibited. This includes removing a table definition entirely or removing a column from a table. Indexes can be removed or added.
+
+## Constraints
+
+- Only `CREATE TABLE` and `CREATE INDEX` are allowed
+- No unique indexes allowed (except for the default primary key unique index that does not need to be created)
+- Non-nullable columns require a default value
+  - This is a cr-sqlite constraint, but in practice w/ Corrosion: it does not matter. Entire changes will be applied all at once and no fields will be missing.
+  - If table schemas are modified, then a default value is definitely required.
+
+## Example
+
+```sql
+-- /etc/corrosion/schema/apps.sql
+
+CREATE TABLE apps (
+    id INT PRIMARY KEY,
+    name TEXT NOT NULL DEFAULT "",
+    user_id INT NOT NULL DEFAULT 0,
+);
+
+CREATE INDEX apps_user_id ON apps (user_id);
+```