Improve README

Author: esimonov

README.md

@@ -40,22 +40,89 @@ func someFunc() {
 	if err != nil {
 		otherFunc2(err)
 	}
-	otherFunc3(err) // Variable referenced in a call outside the if-statement.
+	otherFunc3(err) // Variable referenced in a call outside if-statement.
 }
 ```
 
 ```go
-func someFunc() {
-	sliceOfStrings := getSliceOfStrings()
+func someFunc() interface{} {
+	v := getValue()
+	if v != nil {
+		otherFunc(v)
+	}
+	return v // Variable referenced in return statement.
+}
+```
 
-	if sliceOfStrings == 1 && sliceOfStrings[0] == "" {
-		return
+```go
+func someFunc() interface{} {
+	a, b := getTwoValues()
+	if a != nil {
+		return a
 	}
+	return b // Variables a and b are used in different statements.
+}
+```
 
-	for _, s := range sliceOfStrings { // Variable referenced in a loop.
-		// do stuff
+```go
+func someFunc() {
+	v := &someStruct{}
+
+	if v != nil { // cannot be `if v := &someStruct{}; v != nil
+		return
 	}
 }
 ```
+etc.
 
-etc.
+## Usage
+
+```shell
+usage: ifshort [--max-decl-chars {integer}] [--max-decl-lines {integer}] [INPUT]
+
+positional arguments:
+  INPUT
+
+options:
+  --max-decl-chars
+        maximum length of variable declaration measured in number of characters, after which the linter won't suggest using short syntax. (default 30)
+  --max-decl-lines
+        maximum length of variable declaration measured in number of lines, after which the linter won't suggest using short syntax.  (default 1)
+		Has precedence over max-decl-chars.
+```
+
+Example usage to check only the variables whose declaration takes no more than 50 characters:
+
+`ifshort --max-decl-chars 50 path/to/myproject`.
+
+With this configuration, `ifshort` won't suggest using short syntax on line 3:
+
+```go
+1 func someFunc() {
+2	v := getValue("Long long long declaration, linter shouldn't force short syntax for it.") // More than 50 characters long.
+3	if v != nil {
+4		otherFunc1(v)
+5	}
+6 }
+```
+
+Example usage to check only the variables whose declaration takes no more than 2 lines:
+
+`ifshort --max-decl-lines 2 path/to/myproject`.
+
+```go
+func someFunc() {
+	v1 := getValue("firstLine",
+		    "secondLine") // This declaration will be checked, and short syntax suggested.
+	if v1 != nil {
+		someFunc(v1)
+	}
+
+	v2 := getValue("firstLine",
+			"secondLine",
+			"thirdLine") // This declaration won't be checked.
+	if v2 != nil {
+		someFunc(v2)
+	}
+}
+```