Update README with v4 preview install instructions (#2750)

Author: anthonychu

README.md

@@ -18,19 +18,31 @@ The Azure Functions Core Tools provide a local development experience for creati
 
 **v3**: (v3.x branch): Self-contained cross-platform package **(recommended)**
 
+**v4**: (v4.x branch): Self-contained cross-platform package (preview)
+
 ## Installing
 
 ### Windows
 
 #### To download and install with MSI:
 
+##### v4 (preview)
+
+- [Windows 64-bit](https://go.microsoft.com/fwlink/?linkid=2174087) (VS Code debugging requires 64-bit)
+- [Windows 32-bit](https://go.microsoft.com/fwlink/?linkid=2174159)
+
 ##### v3
 
 - [Windows 64-bit](https://go.microsoft.com/fwlink/?linkid=2135274) (VS Code debugging requires 64-bit)
 - [Windows 32-bit](https://go.microsoft.com/fwlink/?linkid=2135275)
 
 #### To install with npm:
 
+##### v4 (preview)
+```bash
+npm i -g azure-functions-core-tools@4 --unsafe-perm true
+```
+
 ##### v3
 ```bash
 npm i -g azure-functions-core-tools@3 --unsafe-perm true
@@ -43,6 +55,11 @@ npm i -g azure-functions-core-tools@2 --unsafe-perm true
 
 #### To install with chocolatey:
 
+##### v4 (preview)
+```bash
+choco install azure-functions-core-tools-4
+```
+
 ##### v3
 ```bash
 choco install azure-functions-core-tools-3
@@ -62,6 +79,13 @@ choco install azure-functions-core-tools-2
 
 #### Homebrew:
 
+#### v4 (preview)
+    
+```bash
+brew tap azure/functions
+brew install azure-functions-core-tools@4
+```
+
 ##### v3
 ```bash
 brew tap azure/functions
@@ -135,6 +159,12 @@ sudo chown root:root /etc/apt/sources.list.d/microsoft-prod.list
 
 #### 2. Install
 
+##### v4 (preview)
+```bash
+sudo apt-get update
+sudo apt-get install azure-functions-core-tools-4
+```
+
 ##### v3
 ```bash
 sudo apt-get update