[2.7] bpo-30964: Mention ensurepip in package installation docs (GH-2795)

Adds a new 'Pip not installed' section that covers
running `ensurepip` manually, and also references
the relevant section of the Python Packaging User
Guide.

(cherry picked from commit b3527bfefd7a0188d43a2d7515ac6addd97a8202)
diff --git a/Misc/ACKS b/Misc/ACKS
index 35c77b6..662db9f 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -739,6 +739,7 @@
 Lenny Kneler
 Pat Knight
 Jeff Knupp
+Nicholas Kobald
 Kubilay Kocak
 Greg Kochanski
 Manvisha Kodali