Describe how to install the Rust Language Server (#94)

doc/rls_mode/main.md

@@ -14,39 +14,96 @@ The type of the parameter is an object with the following fields:
 
 By default, it is `null`.
 
-### Debugging
+## Setting up
 
-There is an output channel named "Rust Language Server" which is used to show messages from RLS.
+First of all, you have to download the [RLS](https://github.com/rust-lang-nursery/rls) sources:
 
-To open it, perform the following steps:
+```bash
+git clone https://github.com/rust-lang-nursery/rls
+```
 
-* Click "View" on the menu
-* Click "Output" on submenu
-* Click on the listbox which is to the right of the shown panel
-* Choose "Rust Language Server"
+Depending on whether you have rustup or not, there are different ways you can set up this plugin.
+
+* [Setting up with rustup](#with-rustup)
+* [Setting up without rustup](#without-rustup)
+
+#### With rustup
+
+Make sure you do have [rustup](https://github.com/rust-lang-nursery/rustup.rs) with nightly toolchain.
+
+You can use RLS either installed or by running it from the source code.
 
-For making RLS print more data, refer the "Debug RLS" section below.
+If you want use RLS installed, but RLS hasn't been installed yet, perform the following steps in order to install RLS:
 
-### Examples
+```bash
+cd /path/to/rls
+cargo install
+```
 
-#### RLS is installed
+Because at the moment RLS links to the compiler and it assumes the compiler to be globally installed, one has to use rustup to start the `rls` (rustup will configure the environment accordingly):
+
+```json
+"rust.rls": {
+    "executable": "rustup",
+    "args": ["run", "nightly", "rls"]
+}
+```
+
+--
+
+You can also run from source by passing `+nightly` to rustup's cargo proxy:
+
+```json
+"rust.rls": {
+    "executable": "cargo",
+    "args": ["+nightly", "run", "--manifest-path=/path/to/rls/Cargo.toml", "--release"]
+}
+```
+
+#### Without rustup
+
+**Note:** You should do this only if you do not have rustup because otherwise rustup will not work anymore.
+
+After you have cloned the sources, you need to download the latest nightly compiler. See the [Building section of the Rust repository](https://github.com/rust-lang/rust#building-from-source) for how to do this.
+
+You can now install the Rust Language Server globally with
+
+```bash
+cd /path/to/rls
+cargo install
+```
+
+and set `"executable"` to `"rls"`:
 
 ```json
 "rust.rls": {
     "executable": "rls"
 }
 ```
 
-#### Source code of RLS is available
+--
+
+If you don't want to have it installed you can also run it from sources:
 
 ```json
 "rust.rls": {
     "executable": "cargo",
-    "args": ["run", "--manifest-path=/path/to/rls/Cargo.toml"]
+    "args": ["run", "--manifest-path=/path/to/rls/Cargo.toml", "--release"]
 }
 ```
 
-#### Debug RLS
+## Debugging
+
+There is an output channel named "Rust Language Server" which is used to show messages from RLS.
+
+To open it, perform the following steps:
+
+* Click "View" on the menu
+* Click "Output" on submenu
+* Click on the listbox which is to the right of the shown panel
+* Choose "Rust Language Server"
+
+For making RLS print more data, you have to add the following lines to your `"rust.rls"` configuration:
 
 ```json
 "rust.rls": {