doc/install: update Rust info in generic install overview

doc/userguide/install.rst

@@ -16,8 +16,8 @@ Installing from the source distribution files gives the most control over the Su
 
 Basic steps::
 
-    tar xzvf suricata-4.0.0.tar.gz
-    cd suricata-4.0.0
+    tar xzvf suricata-4.1.0.tar.gz
+    cd suricata-4.1.0
     ./configure
     make
     make install
@@ -55,9 +55,10 @@ Common configure options
 
     Enables GeoIP support for detection.
 
-.. option:: --enable-rust
+.. option:: --disable-rust
 
-    Enables experimental Rust support
+    Disables Rust support. Rust support is enabled by default if rustc/cargo
+    are available.
 
 Dependencies
 ^^^^^^^^^^^^
@@ -74,10 +75,14 @@ For full features, also add:
 
   libjansson, libnss, libgeoip, liblua5.1, libhiredis, libevent
 
-Rust support (experimental):
+Rust support:
 
   rustc, cargo
 
+  Not every distro provides Rust packages yet. Rust can also be installed
+  directly from the Rust project itself:
+  https://www.rust-lang.org/en-US/install.html
+
 Ubuntu/Debian
 """""""""""""