change build info

Author: ctapmex

Diff for: README.md

@@ -1,6 +1,25 @@
 # Calculator
 Advanced configurable calculator, plugin for Far Manager 3.
 
+## How to build from source
+To build plugin from source, you will need:
+
+* Visual Studio 2019
+* cmake 3.15 (included in Visual Studio 2019)
+
+#### Release
+From root of source call `vc.build.release.cmd`. The build result will be in ./bin folder.
+
+#### Debug or develop
+For example: 
+```
+call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat" x64
+mkdir cmake-build-debug
+cd cmake-build-debug
+cmake .. -DCMAKE_BUILD_TYPE=Debug -G "Visual Studio 16 2019"
+Calculator.sln
+```
+
 # Common info
 * Extracted from: https://github.com/FarPlugins/farplug-alvls 
 * PlugRing page: https://plugring.farmanager.com/plugin.php?pid=15