Update library dependencies

Libcurl was not listed in the list of required packages.

The tarball installation instruction did not list any of the required
libraries.

Documentation/Getting-Started/Building-MaxScale-from-Source-Code.md

@@ -6,6 +6,7 @@ requirements are as follows:
 * CMake version 2.8 or later (Packaging requires version 2.8.12 or later)
 * GCC version 4.4.7 or later
 * libaio
+* libcurl
 * OpenSSL
 * Bison 2.7 or later
 * Flex 2.5.35 or later

Documentation/Getting-Started/Install-MariaDB-MaxScale-Using-a-Tarball.md

@@ -2,6 +2,12 @@
 
 MariaDB MaxScale is also made available as a tarball, which is named like `maxscale-x.y.z.OS.tar.gz` where `x.y.z` is the same as the corresponding version and `OS` identifies the operating system, e.g. `maxscale-2.0.1.centos.7.tar.gz`.
 
+In order to use the tarball, the following libraries are required:
+
+- libcurl
+- libaio
+- OpenSSL
+
 The tarball has been built with the assumption that it will be installed in `/usr/local`. However, it is possible to install it in any directory, but in that case MariaDB MaxScale must be invoked with a flag.
 
 ## Installing as root in `/usr/local`