Adds some info on compiler

Author: Pavithra K

content/pluginsapi/compiler.md

@@ -3,14 +3,67 @@ title: Compiler
 sort: 2
 ---
 
-## Compiler
+The `Compiler` module of webpack is the main engine that creates a compilation instance with all the options passed through webpack CLI or `webpack` api or webpack comfiguration file.
+
+It is exported by `webpack` api under `webpack.Compiler`.
+
+The compiler is used by webpack by instantiating it and then calling the `run` method.
+
+[__compiler-examples__](https://github.com/pksjce/webpack-internal-examples/blob/master/compiler-example.js)
+
+```javascript
+// Can be imported from webpack package
+import {Compiler} from 'webpack';
+
+// Create a new compiler instance
+const compiler = new Compiler();
+
+// Populate all required options
+compiler.options = {...};
+
+// Creating a plugin.
+class LogPlugin {
+    apply (compiler) {
+        compiler.plugin('should-emit', compilation => {
+            console.log('should i emit');
+            return true;
+        })
+    }
+}
+
+// Apply the compiler to the plugin
+new LogPlugin().apply(compiler);
+
+/* Add other supporting plugins */
+
+// Callback to be executed after run is complete
+const callback = () => {
+    console.log('Compiler has finished execution.')
+};
+
+// call run on the compiler along with the callback
+compiler.run(callback);
+```
+
+?>TODO: Add more explanation of how above code works explaining compiler parts and hooks.
+Also tell Tapable is mixed in with Compiler.Differentiate between Compiler's and Tapable's methods
 
 ## Watching
 
+?>TODO: Add that compiler duplicates all above functionality and adds watch functionality to it. Highlight differences.
+
 ## MultiCompiler
 
+?> Can create child compilers?
+
 ## Event Hooks
 
+?>TODO: For each hook follow template of
+1. event name
+2. reason for event.
+3. async or sync or parallel or waterfall
+4. some usage examples.
+
 `environment()`
 
 `after-environment()`