Added instructions for using in SublimeText with the LSP plugin

Using_in_sublime_text.md

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+# Using Microsoft Python Language Server with Sublime Text
+
+## Prerequisites
+
+* A build of the Microsoft Python Language Server (MPLS hereinafter)
+* .NET Core 2.1 Runtime installed
+* Sublime Text 3 (Tested with build 3176)
+* [LSP plugin](https://github.com/tomv564/LSP)
+
+## Sublime Text configuration
+
+This procedure has been tested on Windows 10 April 2018 Update but should also
+work on Linux and Mac if you change the paths accordingly. This also assumes
+you have a build of MPLS in C:\\python-language-server (again, change the path
+on other platforms).
+
+* Edit LSP.sublime-settings - User adding the following:
+
+```json
+{
+    "clients":
+    {
+        "mspyls":
+        {
+            "command": [ "dotnet.exe", "exec", "C:\\python-language-server\\Microsoft.Python.LanguageServer.dll" ],
+            "scopes": ["source.python"],
+            "syntaxes": ["Packages/Python/Python.sublime-syntax"],
+            "languageId": "python",
+            "initializationOptions": 
+            {
+                "interpreter": 
+                {
+                    "properties": 
+                    {
+                        "UseDefaultDatabase": true,
+                        "Version": "3.7"
+                    }                    
+                }
+            }
+        }
+    }
+}
+```
+
+Remember to set the "command" path accordingly to your setup. Also set the
+"Version" field ("3.7" in the example above) to the version of the python
+interpreter you have in your path. If you don't have a python interpreter in
+your PATH env var, add a "InterpreterPath" field alongside "Version" and set
+it to the path of your python installation. At this point you can just enable
+the language server (refer to LSP documentation on how to do it) and your good
+to go.
+
+## Virtual environments
+
+If you use sublime text projects and have different virtual environment for your
+projects you can add the following to your project file (your-project.sublime-
+project):
+
+```json
+{
+    "settings":
+    {
+        "LSP":
+        {
+            "mspyls":
+            {
+                "enabled": true,
+                "initializationOptions": 
+                {
+                    "interpreter": 
+                    {
+                        "properties": 
+                        {
+                            "InterpreterPath": "path_to_your_virtual_env\\python.exe",
+                            "UseDefaultDatabase": true,
+                            "Version": "the_version_of_python_in_your_virtual_env"
+                        }                    
+                    }
+                }
+            }
+        }
+    }
+}
+
+```
+
+The language server will then pick the interpreter in your virtual environment.