Added usage documentation for optional installs

README.rst

@@ -59,6 +59,13 @@ Installation
 
 -  ``python -m pip install sanic``
 
+To install sanic without uvloop or json using bash, you can provide either or both of these environmental variables
+using any truthy string like `'y', 'yes', 't', 'true', 'on', '1'` and setting the NO_X to true will stop that features
+installation.
+
+- ``SANIC_NO_UVLOOP=true SANIC_NO_UJSON=true python -m pip install sanic``
+
+
 Documentation
 -------------