doc: Explain $LIB in LD_PRELOAD in gitian descriptors

contrib/gitian-descriptors/gitian-linux.yml

@@ -59,6 +59,7 @@ script: |
     mkdir -p ${BASE_CACHE} ${SOURCES_PATH}
   fi
 
+  # Use $LIB in LD_PRELOAD to avoid hardcoding the dir (See `man ld.so`)
   function create_global_faketime_wrappers {
   for prog in ${FAKETIME_PROGS}; do
     echo '#!/usr/bin/env bash' > ${WRAP_DIR}/${prog}

contrib/gitian-descriptors/gitian-osx.yml

@@ -55,6 +55,7 @@ script: |
 
   export ZERO_AR_DATE=1
 
+  # Use $LIB in LD_PRELOAD to avoid hardcoding the dir (See `man ld.so`)
   function create_global_faketime_wrappers {
   for prog in ${FAKETIME_PROGS}; do
     echo '#!/usr/bin/env bash' > ${WRAP_DIR}/${prog}

contrib/gitian-descriptors/gitian-win.yml

@@ -48,6 +48,7 @@ script: |
     mkdir -p ${BASE_CACHE} ${SOURCES_PATH}
   fi
 
+  # Use $LIB in LD_PRELOAD to avoid hardcoding the dir (See `man ld.so`)
   function create_global_faketime_wrappers {
   for prog in ${FAKETIME_PROGS}; do
     echo '#!/usr/bin/env bash' > ${WRAP_DIR}/${prog}