Update BUILDING.txt to document GnuTLS requirements
See Issue #44 for further details.
diff --git a/BUILDING.txt b/BUILDING.txt
index 8f686cc..e26073c 100644
--- a/BUILDING.txt
+++ b/BUILDING.txt
@@ -15,6 +15,7 @@
-- If building TLS support:
* GnuTLS
+ * See "Building TLS Support" below.
-- If building native language support (NLS):
* Gnu gettext 0.14.4 or later
@@ -322,6 +323,28 @@
======================================
+Building TLS Support
+======================================
+
+TLS requires GnuTLS, which is supplied with most Linux distributions and
+with MinGW for Windows and can be built from source on OS X and other
+Unix variants. However, GnuTLS versions > 2.12.x && < 3.3.x should be
+avoided because of potential incompatibilities during initial handshaking.
+
+You can override the GNUTLS_LIBRARY and GNUTLS_INCLUDE_DIR CMake variables
+to specify the locations of libgnutls and any dependencies. For instance,
+adding
+
+ -DGNUTLS_INCLUDE_DIR=/usr/local/include \
+ -DGNUTLS_LIBRARY="/usr/local/lib/libgnutls.a; \
+ /usr/local/lib/libgcrypt.a; \
+ /usr/local/lib/libgpg-error.a"
+
+to the CMake command line would link TigerVNC against a static version of
+libgnutls located under /usr/local.
+
+
+======================================
Building Native Language Support (NLS)
======================================