Add requirement

bazel/README.md

@@ -20,6 +20,7 @@ Dockers [Alpine, Archlinux, Centos, Debian, Fedora, OpenSuse, Ubuntu]: [![Status
 ## Introduction
 
 <nav for="bazel"> |
+<a href="#requirement">Requirement</a> |
 <a href="#dependencies">Dependencies</a> |
 <a href="#compilation">Compilation</a> |
 <a href="#testing">Testing</a> |
@@ -34,6 +35,11 @@ you can download it for free from <https://bazel.build/>.
 **warning: Currently OR-Tools Bazel doesn't support Python, Java nor .Net,
 please use the Makefile or CMake based build instead.**
 
+## Requirement
+You'll need:
+
+* `Bazel >= 4.0`.
+
 ## Dependencies
 
 OR-Tools depends on severals mandatory libraries.

cmake/README.md

@@ -40,7 +40,8 @@ Dockers [Alpine, Archlinux, Centos, Debian, Fedora, OpenSuse, Ubuntu]x[C++, Pyth
 
 ## Introduction
 <nav for="cmake"> |
-<a href="#deps">Dependencies</a> |
+<a href="#requirement">Requirement</a> |
+<a href="#dependencies">Dependencies</a> |
 <a href="#options">Options</a> |
 <a href="docs/cpp.md">C++</a> |
 <a href="docs/swig.md">Swig</a> |
@@ -61,7 +62,10 @@ the compiler environment of your choice.<br>You can either build OR-Tools with
 CMake as a standalone project or it can be incorporated into an existing CMake
  project.
 
-<a name="deps"></a>
+## Requirement
+You'll need:
+
+* `CMake >= 3.15` (`3.18` for python support).
 
 ## Dependencies
 

makefiles/README.md

@@ -40,14 +40,20 @@ Python, Java, .Net]: [![Status][docker_svg]][docker_link]
 
 ## Introduction
 <nav for="make"> |
-<a href="#deps">Dependencies</a> |
+<a href="#requirement">Requirement</a> |
+<a href="#dependencies">Dependencies</a> |
 <a href="docs/ci.md">CI</a> |
 </nav>
 
 OR-Tools comes with a GNU Make based build ([Makefile](../Makefile)) that can be
 used on a wide range of platforms.
 
-## [Dependencies](#deps)
+## Requirement
+You'll need:
+
+* `GNU Make >= 4.3`.
+
+## Dependencies
 
 OR-Tools depends on severals mandatory libraries. You can compile them all using
 the target `third_party` or you can compile few of them and give the