Add a possible issue to the README.

Author: theindigamer

README.md

@@ -23,6 +23,16 @@ fn main() {
 }
 ```
 
+**NOTE:** The computed width values may not match the actual rendered column
+width. For example, the woman scientist emoji comprises of a woman emoji, a
+zero-width joiner and a microscope emoji.
+
+```rust
+    assert_eq!(UnicodeWidthStr::width("👩"), 2); // Woman
+    assert_eq!(UnicodeWidthStr::width("🔬"), 2); // Microscope
+    assert_eq!(UnicodeWidthStr::width("👩‍🔬"), 4); // Woman scientist
+```
+
 ## features
 
 unicode-width does not depend on libstd, so it can be used in crates

src/tests.rs

@@ -108,6 +108,16 @@ fn test_str() {
     assert_eq!("\u{2081}\u{2082}\u{2083}\u{2084}".width_cjk(), 8);
 }
 
+#[test]
+fn test_emoji() {
+    // Example from the README.
+    use super::UnicodeWidthStr;
+
+    assert_eq!(UnicodeWidthStr::width("👩"), 2); // Woman
+    assert_eq!(UnicodeWidthStr::width("🔬"), 2); // Microscope
+    assert_eq!(UnicodeWidthStr::width("👩‍🔬"), 4); // Woman scientist
+}
+
 #[test]
 fn test_char() {
     use super::UnicodeWidthChar;