Update readme

Author: kolen

README.md

@@ -3,7 +3,26 @@
 [Slim](http://slim-lang.com/) template grammar for
 [tree-sitter](https://tree-sitter.github.io/).
 
-**Completeness**: something works, but still early stage, not usable
+Alpha-stage, parses most cases, but syntax tree structure isn't
+stabilized yet, prone to changes.
+
+## Limitations
+
+Slim is [highly
+configurable](https://rubydoc.info/gems/slim/frames#configuring-slim)
+and some of configuration parameters change syntax. Tree-sitter does
+not support dynamically generated syntax, so this grammar is not
+configurable. It should work for default settings and some subset of
+customized settings.
+
+- `tabsize`: always 4, should work with other values if you don't mix spaces and tabs in the same file
+- `encoding`: always utf-8 (some unicode features don't work yet)
+- `shortcut`: some of shortcuts work `TODO: describe`
+- `code_attr_delims`: only default is supported, `() [] {}`
+- `attr_list_delims`: only default is supported, `() [] {}`
+- `enable_engines`: TODO
+- `disable_engines`: TODO
+- `splat_prefix`: only default is supported, `*`
 
 ## Grammar references