Make it clearer that HOL master should be used

Author: myreen

README.md

@@ -5,7 +5,7 @@ CakeML is a verified implementation of a significant subset of
 Standard ML.
 
 The source and proofs for CakeML are developed in the [HOL4 theorem
-prover](http://hol-theorem-prover.org). We use the latest development
+prover](http://hol-theorem-prover.org). We use the latest master
 version of [HOL4](https://github.com/HOL-Theorem-Prover/HOL), which we
 build on [PolyML 5.7.1](http://www.polyml.org).
 Example build instructions can be found in

build-instructions.sh

@@ -26,10 +26,8 @@ make install
 
 ## build HOL
 cd
-git clone https://github.com/HOL-Theorem-Prover/HOL
+git clone https://github.com/HOL-Theorem-Prover/HOL -b master
 cd HOL
-## optionally switch to a released version, e.g., kananaskis-11
-# git checkout kananaskis-11
 ## note: currently, we only aim to ensure that
 ##       CakeML branch master builds on HOL branch master
 poly --script tools/smart-configure.sml

readmePrefix

@@ -5,7 +5,7 @@ CakeML is a verified implementation of a significant subset of
 Standard ML.
 
 The source and proofs for CakeML are developed in the [HOL4 theorem
-prover](http://hol-theorem-prover.org). We use the latest development
+prover](http://hol-theorem-prover.org). We use the latest master
 version of [HOL4](https://github.com/HOL-Theorem-Prover/HOL), which we
 build on [PolyML 5.7.1](http://www.polyml.org).
 Example build instructions can be found in