docs: add note for non extensibility of hooks (#7160)

Author: snitin315

src/content/api/compilation-hooks.mdx

@@ -11,6 +11,7 @@ contributors:
   - EugeneHlushko
   - chenxsan
   - jamesgeorge007
+  - snitin315
 ---
 
 The `Compilation` module is used by the `Compiler` to create new compilations
@@ -30,6 +31,8 @@ compilation.hooks.someHook.tap(/* ... */);
 As with the `compiler`, `tapAsync` and `tapPromise` may also be available
 depending on the type of hook.
 
+W> Since webpack 5, `hooks` are no longer extendable. Use a `WeakMap` to add custom hooks.
+
 ### buildModule
 
 `SyncHook`

src/content/api/compiler-hooks.mdx

@@ -10,14 +10,17 @@ contributors:
   - EugeneHlushko
   - superburrito
   - chenxsan
+  - snitin315
 ---
 
 The `Compiler` module is the main engine that creates a compilation instance
 with all the options passed through the [CLI](/api/cli) or [Node API](/api/node). It extends the
 `Tapable` class in order to register and call plugins. Most user-facing plugins
 are first registered on the `Compiler`.
 
-When developing a plugin for webpack, you might want to know where each hook is called. To learn this, search for `hooks.<hook name>.call` across the webpack source
+When developing a plugin for webpack, you might want to know where each hook is called. To learn this, search for `hooks.<hook name>.call` across the webpack source.
+
+W> Since webpack 5, `hooks` are no longer extendable. Use a `WeakMap` to add custom hooks.
 
 ## Watching
 

src/content/api/parser.mdx

@@ -8,6 +8,7 @@ contributors:
   - misterdev
   - EugeneHlushko
   - chenxsan
+  - snitin315
 ---
 
 The `parser` instance, found in the `compiler`, is used to parse each module
@@ -36,6 +37,8 @@ depending on the type of hook.
 The following lifecycle hooks are exposed by the `parser` and can be accessed
 as such:
 
+W> Since webpack 5, `hooks` are no longer extendable. Use a `WeakMap` to add custom hooks.
+
 ### evaluateTypeof
 
 `SyncBailHook`