Explicitly say `pthread_cancel` in the docs.

Bug: http://b/33943372
Test: N/A
Change-Id: If71691f7ff20c9b8c14de15692543bbd858c9aab
diff --git a/docs/status.md b/docs/status.md
index c8c06c6..b6439a0 100644
--- a/docs/status.md
+++ b/docs/status.md
@@ -27,7 +27,7 @@
 Missing functionality:
   * `<aio.h>`
   * `<wordexp.h>`
-  * Thread cancellation
+  * Thread cancellation (`pthread_cancel`).
   * Robust mutexes
 
 Run `./libc/tools/check-symbols-glibc.py` in bionic/ for the current