Minor fixes to the README file

README.md

 # dune-perftool
 
-dune-perftool is an active research code project with the goal of
+dune-perftool is an active research project with the goal of
 generating high-performance integration kernels for dune-pdelab.
 
 **Note**: Due to the research character of the code things will change
-a lot and there is no guarantee of interface stability ;).
+a lot and there is no guarantee for interface stability ;).
 
 
 ## Dependencies
@@ -21,7 +21,7 @@ dune-perftool depends on the following software packages:
 
 ## Cloning and Patching
 
-We use several sumbodules so you should clone with the --recursive option:
+We use several submodules so you should clone with the `--recursive` option:
 
 ```
 git clone --recursive ssh://git@parcomp-git.iwr.uni-heidelberg.de:20022/dominic/dune-perftool.git
@@ -33,9 +33,9 @@ or
 git clone --recursive https://parcomp-git.iwr.uni-heidelberg.de/dominic/dune-perftool.git
 ```
 
-If you have a feature branch 'feature/my-branch' where you change the
+If you have a feature branch `feature/my-branch` where you change the
 submodules of dune-perftool and you want to test your branch it makes
-sense to checkout this branch directly:
+sense to checkout this branch directly in a fresh clone:
 
 ```
 git clone --recursive -b feature/my-branch ssh://git@parcomp-git.iwr.uni-heidelberg.de:20022/dominic/dune-perftool.git
@@ -81,7 +81,7 @@ the following:
 
 ```
 CMAKE_FLAGS="
-  -DDUNE_FORCE_PYTHON3=1
+  -DDUNE_PYTHON_FORCE_PYTHON3=1
   -DDUNE_PYTHON_ALLOW_GET_PIP=1
   -DDUNE_PYTHON_VIRTUALENV_SETUP=1
   -DCMAKE_BUILD_TYPE=Release