doc tidy, add snap install plus comment

Author: Dave Conway-Jones

docs/getting-started/installation.md

@@ -32,6 +32,17 @@ Note: <code>sudo</code> is only required during the install when running on Linu
 running on Windows, see the <a href="../platforms/windows">Windows Install instructions</a>.
 </div>
 
+### Install via SNAP
+
+If your OS supports [SNAPs](https://snapcraft.io/docs/core/install) you can install Node-RED with:
+
+    snap install node-red
+
+but please note that this runs in a secure container and so does not have access to any extra facilities
+that may be needed for your use, such as gcc to compile nodes that have native plugins, git (for projects),
+direct access to gpio, any external programs (to call out to), and so on. You can run it in "classic"
+mode, which reduces the container security, but we leave that as an exercise for the reader.
+
 #### Next
 
 Once installed, you are ready to [run Node-RED](running).

docs/getting-started/running.md

@@ -42,7 +42,7 @@ You can now create your [first flow](first-flow).
 
 ### Command-line usage
 
-    Usage: node-red [-v] [-?] [--port PORT] [--safe] [--settings settings.js] 
+    Usage: node-red [-v] [-?] [--port PORT] [--safe] [--settings settings.js]
                     [--title TITLE] [--userDir DIR] [flows.json]
 
     Options:
@@ -53,13 +53,13 @@ You can now create your [first flow](first-flow).
       -u, --userDir DIR    use specified user directory
       -v                   enable verbose output
       -?, --help           show usage
-      flows.json           name of the flow file you want to work with. Using different names, 
-                           such as greenhouse.json or robot.json, you can separate different 
-                           undertakings you are working on. If you don't specify a name, it 
+      flows.json           name of the flow file you want to work with. Using different names,
+                           such as greenhouse.json or robot.json, you can separate different
+                           undertakings you are working on. If you don't specify a name, it
                            defaults to flows_xxx.json where xxx is the hostname of your server.
 
 ----
-                           
+
 #### Running from a local install - Linux & Mac OS X
 
 The `node-red` command can still be accessed even if Node-RED hasn't been installed