guix: add additional documentation to patches

contrib/guix/patches/gcc-8-sort-libtool-find-output.patch

@@ -1,3 +1,11 @@
+guix: repro: Sort find output in libtool for gcc-8
+
+Otherwise the resulting .a static libraries (e.g. libstdc++.a) will not
+be reproducible and end up making the Bitcoin binaries non-reproducible
+as well.
+
+See: https://reproducible-builds.org/docs/archives/#gnu-libtool
+
 diff --git a/gcc/configure b/gcc/configure
 index 97ba7d7d69c..e37a96f0c0c 100755
 --- a/gcc/configure

contrib/guix/patches/glibc-2.24-elfm-loadaddr-dynamic-rewrite.patch

@@ -1,3 +1,5 @@
+https://sourceware.org/git/?p=glibc.git;a=commit;h=a68ba2f3cd3cbe32c1f31e13c20ed13487727b32
+
 commit 6b02af31e9a721bb15a11380cd22d53b621711f8
 Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
 Date:   Wed Oct 18 17:26:23 2017 +0100

contrib/guix/patches/glibc-2.24-no-build-time-cxx-header-run.patch

@@ -1,3 +1,5 @@
+https://sourceware.org/git/?p=glibc.git;a=commit;h=fc3e1337be1c6935ab58bd13520f97a535cf70cc
+
 commit dc23a45db566095e83ff0b7a57afc87fb5ca89a1
 Author: Florian Weimer <fweimer@redhat.com>
 Date:   Wed Sep 21 10:45:32 2016 +0200

contrib/guix/patches/glibc-2.27-riscv64-Use-__has_include__-to-include-asm-syscalls.h.patch

@@ -1,3 +1,5 @@
+https://sourceware.org/git/?p=glibc.git;a=commit;h=0b9c84906f653978fb8768c7ebd0ee14a47e662e
+
 From 562c52cc81a4e456a62e6455feb32732049e9070 Mon Sep 17 00:00:00 2001
 From: "H.J. Lu" <hjl.tools@gmail.com>
 Date: Mon, 31 Dec 2018 09:26:42 -0800

contrib/guix/patches/nsis-SConstruct-sde-support.patch

@@ -1,3 +1,6 @@
+https://github.com/kichik/nsis/pull/13
+https://sourceforge.net/p/nsis/code/7248/
+
 diff --git a/SConstruct b/SConstruct
 index e8252c9..41786f2 100755
 --- a/SConstruct