docs: update README

Signed-off-by: Tom <[email protected]>

Author: tmzane

README.md

@@ -7,9 +7,96 @@
 
 A Go linter that ensures consistent code style when using `log/slog`.
 
+## 📌 About
+
+The `log/slog` API allows two different types of arguments: key-value pairs and attributes.
+People may have different opinions about which one is better,
+but nobody probably wants to mix them up because it makes the code harder to read.
+
+```go
+slog.Info("a user has logged in", "user_id", 42, slog.String("ip_address", "192.0.2.0")) // ugh
+```
+
+`sloglint` finds such function calls and checks that all the arguments are either key-value pairs or attributes.
+The linter has several options, so you can adjust it to your own code style.
+
 ## 🚀 Features
 
-* Forbid mixing key-value pairs and attributes in a single function call (default)
+* Forbid mixing key-value pairs and attributes within a single function call (default)
 * Enforce using either key-value pairs or attributes for the entire project (optional)
 * Enforce using constants instead of raw keys (optional)
 * Enforce putting arguments on separate lines (optional)
+
+## 📦 Install
+
+Download a prebuilt binary from the [Releases][1] page.
+
+## 📋 Usage
+
+```shell
+sloglint [flags] ./...
+```
+
+### Key-value pairs only
+
+The `-kv-only` flag causes `sloglint` to report any use of attributes.
+
+```go
+slog.Info("a user has logged in", slog.Int("user_id", 42)) // sloglint: attributes should not be used
+```
+
+### Attributes only
+
+In contrast, the `-attr-only` flag causes `sloglint` to report any use of key-value pairs.
+
+```go
+slog.Info("a user has logged in", "user_id", 42) // sloglint: key-value pairs should not be used
+```
+
+### No raw keys
+
+To prevent typos, you may want to forbid the use of raw keys altogether.
+The `-no-raw-keys` flag causes `sloglint` to report the use of strings as keys (including `slog.Attr` calls, e.g. `slog.Int("user_id", 42)`).
+
+```go
+slog.Info("a user has logged in", "user_id", 42) // sloglint: raw keys should not be used
+```
+
+This report can be fixed by using either constants...
+
+```go
+const UserId = "user_id"
+
+slog.Info("a user has logged in", UserId, 42)
+```
+
+...or custom `slog.Attr` constructors.
+
+```go
+func UserId(value int) slog.Attr { return slog.Int("user_id", value) }
+
+slog.Info("a user has logged in", UserId(42))
+```
+
+> 💡 Such helpers can be automatically generated for you by the [`sloggen`][2] tool. Give it a try too!
+
+### Arguments on separate lines
+
+To improve code readability, you may want to put arguments on separate lines, especially when using key-value pairs.
+The `-args-on-sep-lines` flag causes `sloglint` to report 2+ arguments on the same line.
+
+```go
+slog.Info("a user has logged in", "user_id", 42, "ip_address", "192.0.2.0") // sloglint: arguments should be put on separate lines
+```
+
+This report can be fixed by reformatting the code.
+
+```go
+slog.Info("a user has logged in",
+    "user_id", 42,
+    "ip_address", "192.0.2.0",
+)
+```
+
+[1]: https://github.com/go-simpler/sloglint/releases
+[2]: https://github.com/go-simpler/sloggen