minor #11115 Added a note about virtual machine for local build (Jules Pietri)

This PR was merged into the 3.4 branch.

Discussion
----------

Added a note about virtual machine for local build

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/roadmap for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `master` for features of unreleased versions).

-->

Commits
-------

091bb22 Added a note about virtual machine for local build

Author: javiereguiluz

README.markdown

@@ -33,3 +33,6 @@ $ docker build . -t symfony-docs
 # (if it's already in use, change the '8080' port by any other port)
 $ docker run --rm -p 8080:80 symfony-docs
 ```
+
+If you use a virtual machine use its ip instead of the localhost to access the
+server (i.e `http://192.168.99.100:8080`).