python3-filelock: Install docs/how-to.rst for ptests

test_documented_cache_lock_name reads docs/how-to.rst relative to the
tests dir and fails with FileNotFoundError when it is not installed.

Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>

meta-python/recipes-devtools/python/python3-filelock_4.2.4.bb

@@ -40,4 +40,6 @@ RDEPENDS:${PN}-ptest += " \
 do_install_ptest:append() {
     cp -rf ${S}/tasks ${D}${PTEST_PATH}/
     cp -f ${S}/pyproject.toml ${D}${PTEST_PATH}/
+    # test_documented_cache_lock_name checks snippets in docs/how-to.rst
+    install -Dm 0644 ${S}/docs/how-to.rst ${D}${PTEST_PATH}/docs/how-to.rst
 }