Update docs

docs/usage/commands.mdx

@@ -27,6 +27,8 @@ as modules with `Ctrl + a`.
 You can also mark your Python [source roots](configuration#source-roots) by pressing `s`.
 This allows Tach to understand module paths and correctly identify first-party imports.
 
+You can mark modules as [utilities](configuration#modules) by pressing `u`. This is appropriate for modules like `utils/`, which can be freely used by the rest of the code.
+
 To save your modules, use `Ctrl + s`. Otherwise, to exit without saving, use `Ctrl + c`.
 
 Any time you make changes with `tach mod`, run [`tach sync`](commands#tach-sync)

docs/usage/configuration.mdx

@@ -49,6 +49,12 @@ path = "tach.__main__"
 depends_on = [{ path = "tach.start" }]
 strict = true
 
+[[modules]]
+path = "tach.errors"
+depends_on = []
+strict = true
+utility = true
+
 [[modules]]
 path = "tach.parsing"
 depends_on = [{ path = "tach" }, { path = "tach.filesystem" }]
@@ -58,7 +64,6 @@ strict = true
 [[modules]]
 path = "tach.check"
 depends_on = [
-    { path = "tach.errors" },
     { path = "tach.extension" },
     { path = "tach.filesystem" },
     { path = "tach.parsing" },
@@ -81,7 +86,8 @@ Each module listed under the `modules` key above can accept the following attrib
 - `path`: the Python import path to the module (e.g. `a.b` for `<root>/a/b.py`)
 - `depends_on`: a list of the other modules which this module can import from (default: `[]`)
 - `visibility`: a list of other modules which can import from this module (default: `['*']`)
-- `strict`: enables [strict mode](strict-mode) for the module
+- `strict`: enables [strict mode](strict-mode) for the module (boolean)
+- `utility`: marks this module as a **Utility**, meaning all other modules may import from it without declaring an explicit dependency (boolean)
 
 <Note>
   Tach also supports [deprecating individual dependencies](../usage/deprecate).

docs/usage/faq.mdx

@@ -21,6 +21,22 @@ To prevent any external usage of a given module, you can set `visibility: []` fo
 
 [See more information on configuration here.](./configuration)
 
+### How can I declare modules which are freely usable by the rest of the code?
+
+This is typically done for modules like `utils/`, `errors/` or `lib/`, which contain relatively isolated code which can be used throughout a project.
+
+Tach allows marking these modules as **Utilities**, which means they can be used without being listed as an explicit dependency.
+
+<Note>
+  Marking a module with `utility: true` is different from `visibility: ['*']`.
+  Even when a module has public visibility, other modules must declare an
+  explicit dependency to use it (in fact, modules are publicly visible by
+  default). In contrast, a utility module does not require its dependents to
+  list an explicit dependency.
+</Note>
+
+[See more information on configuration here.](./configuration)
+
 ### Are conditional imports checked?
 
 Tach will check all imports in your source files, including those which are called conditionally.