Fix Markdown anchor issue (#711)

Signed-off-by: Dscano <d.scano89@gmail.com>

Author: Dscano

README.md

@@ -6,10 +6,10 @@
 * [Introduction](#introduction)
 * [Presentation](#presentation)
 * [P4 Documentation](#p4-documentation)
-* [P4Sim] (#p4sim)
+* [P4sim](#p4sim--a-simple-p4-behavioral-simulator)
 * [Obtaining required software](#obtaining-required-software)
-     * [To build the virtual machine](#to-build-the-virtual-machine)
-     * [Accessing the VM](#accessing-the-vm)
+     * [To build the virtual machine](#to-build-a-virtual-machine-with-the-p4-development-tools)
+     * [Accessing the VM](#download-a-virtual-machine-with-the-p4-development-tools-already-installed)
      * [To install P4 development tools on an existing system](#to-install-p4-development-tools-on-an-existing-system)
 * [How to Contribute](#how-to-contribute)
 * [Older tutorials](#older-tutorials)