docs: clarify CMake requirements for build and test commands

Keep the CMake 3.10 project minimum while documenting the newer CLI requirements. Add a build-directory/install-target alternative for older CMake and state the CTest requirement in the test guide.

Validation: shell examples pass bash -n; local documentation links resolve.
Signed-off-by: Denys Fedoryshchenko <denys.f@collabora.com>

2 files changed, 19 insertions, 0 deletions

diff --git a/README.md b/README.md
index af678b9e..bac35421 100644
--- a/README.md
+++ b/README.md
@@ -57,12 +57,26 @@ Building and installing
 
 Use an out-of-tree build directory:
 
+The commands below require CMake 3.15 or newer: -S/-B were added in 3.13,
+and --install was added in 3.15. The project itself still supports CMake 3.10.
+
     cmake -S . -B build \
       -DCMAKE_BUILD_TYPE=Release \
       -DCMAKE_INSTALL_PREFIX=/usr/local
     cmake --build build
     sudo cmake --install build
 
+For CMake 3.10 through 3.14, use the build-directory form and the generated
+install target instead:
+
+    mkdir -p build
+    cd build
+    cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr/local ..
+    cmake --build .
+    sudo cmake --build . --target install
+
+Run the remaining examples from the repository root.
+
 Useful build options:
 
 * BUILD_IPOE_DRIVER=TRUE builds the IPoE kernel module.
diff --git a/tests/README.md b/tests/README.md
index 870cf8c8..ac8d016b 100644
--- a/tests/README.md
+++ b/tests/README.md
@@ -2,6 +2,11 @@
 
 These tests are done for Ubuntu and Debian distros. Please use latest stable Debian or Ubuntu to run the tests.
 
+The commands in this guide require CMake/CTest 3.20 or newer, including
+`ctest --test-dir`. The standalone kernel-module installation script requires
+CMake 3.15 or newer for `cmake --install`. These command requirements are
+separate from the project's minimum CMake version of 3.10.
+
 ## Focused unit tests
 
 The standalone unit tests compile production callbacks with small test fixtures