Add URLs for random engine specifications to global.ent

see php/doc-en#1922

Closes GH-76.

Author: TimWolla

entities/global.ent

@@ -383,6 +383,9 @@
 <!ENTITY url.tcadb "http://fallabs.com/tokyocabinet/">
 <!ENTITY url.qmail "http://cr.yp.to/qmail.html">
 <!ENTITY url.quickzip "http://www.quickzip.org/">
+<!ENTITY url.random.mersenne-twister "http://www.math.sci.hiroshima-u.ac.jp/m-mat/MT/ARTICLES/mt.pdf">
+<!ENTITY url.random.pcg "https://www.pcg-random.org/">
+<!ENTITY url.random.xoshiro "https://prng.di.unimi.it/">
 <!ENTITY url.rar "http://www.rarlabs.com/">
 <!ENTITY url.readline "http://cnswww.cns.cwru.edu/~chet/readline/rltop.html">
 <!ENTITY url.readline.windows "http://mingweditline.sourceforge.net/">