re-add the word debian, oops

Author: reaperhulk

docs/installation.rst

@@ -17,7 +17,7 @@ PyPy 5.3+ on these operating systems.
 * x86-64 FreeBSD 11
 * macOS 10.12 Sierra, 10.11 El Capitan
 * x86-64 Ubuntu 14.04, 16.04, and rolling
-* x86-64 Jessie (8.x), Stretch (9.x), Buster, and Sid (unstable)
+* x86-64 Debian Jessie (8.x), Stretch (9.x), Buster, and Sid (unstable)
 * x86-64 Alpine (latest)
 * 32-bit and 64-bit Python on 64-bit Windows Server 2012