Update README.rst

Minor corrections and advice... Should help beginners.

README.rst

@@ -259,20 +259,24 @@ to install using pip and a virtualenv::
     python3 -m venv ./env
     source ./env/bin/activate
     pip install -e ".[all,test]"
-
+    
 This will run a process of downloading and installing all the needed
 dependencies into a virtual env.
 
+Some of the dependencies might have to be installed manually, if you run into errors just install the dependency that is mentioned in the error manually.
+
 Once this is done, you may wish to run Synapse's unit tests, to
 check that everything is installed as it should be::
 
     python -m twisted.trial tests
 
 This should end with a 'PASSED' result::
 
-    Ran 1266 tests in 643.930s
+    Ran 1332 tests in 716.064s
+
+    PASSED (skips=15, successes=1317)
 
-    PASSED (skips=15, successes=1251)
+(The amount of tests may change in the future...)
 
 Running the Integration Tests
 =============================