Update BUILD.md

BUILD.md

@@ -39,7 +39,7 @@ Okay, now let's get the tools and libraries for building and installing Shairpor
 # apt upgrade # this is optional but recommended
 # apt install --no-install-recommends build-essential git xmltoman autoconf automake libtool \
     libpopt-dev libconfig-dev libasound2-dev avahi-daemon libavahi-client-dev libssl-dev libsoxr-dev \
-    libplist-dev libsodium-dev libavutil-dev libavcodec-dev libavformat-dev uuid-dev xxd
+    libplist-dev libsodium-dev libavutil-dev libavcodec-dev libavformat-dev uuid-dev libgcrypt-dev xxd
 ```
 If you are building classic Shairport Sync, the list of packages is shorter:
 ```
@@ -54,7 +54,7 @@ For AirPlay 2 operation, _before you install the libraries_, please ensure the y
 # yum update
 # yum install make automake gcc gcc-c++ \
     git xmltoman autoconf automake avahi-devel libconfig-devel openssl-devel popt-devel soxr-devel \
-    ffmpeg ffmpeg-devel libplist-devel libsodium-devel libuuid-devel vim-common \
+    ffmpeg ffmpeg-devel libplist-devel libsodium-devel libgcrypt-dev libuuid-devel vim-common \
     alsa-lib-devel
 ```
 If you are building classic Shairport Sync, the list of packages is shorter: