man: Document the tar entry size limitation for deb(5) format

debian/changelog

@@ -5,6 +5,7 @@ dpkg (1.18.8) UNRELEASED; urgency=medium
     - Improve dpkg-buildpackage(1) on environment expectations.
     - Clarify the format of the db:Status-Abbrev virtual field in
       dpkg-query(1). Closes: #824515
+    - Document the tar entry size limitation for deb(5) format.
 
   [ Updated programs translations ]
   * German (Sven Joachim).

man/deb.5

@@ -49,6 +49,8 @@ the pre-POSIX ustar format, a subset of the GNU format (only the new
 style long pathnames and long linknames, supported since dpkg 1.4.1.17),
 and the POSIX ustar format (long names supported since dpkg 1.15.0).
 Unrecognized tar typeflags are considered an error.
+Each tar entry size inside a tar archive is limited to 11 ASCII octal
+digits, allowing for up to 8 GiB tar entries.
 .PP
 The first member is named
 .B debian\-binary