Update CHANGELOG.md for 3.6.0

Update CHANGELOG for 3.6.0 and collect Tested-by tags.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Tested-by: Jens Wiklander <jens.wiklander@linaro.org> (Juno)
Tested-by: Sumit Garg <sumit.garg@linaro.org> (Developerbox)
Tested-by: Jerome Forissier <jerome.forissier@linaro.org> (HiKey960, GP)
Tested-by: Rouven Czerwinski <r.czerwinski@pengutronix.de> (mx6qsabresd)
Tested-by: Etienne Carriere <etienne.carriere@linaro.org> (b2120, b2260, GP)
Tested-by: Volodymyr Babchuk <vlad.babchuk@gmail.com> (RCAR H3)
Tested-by: Volodymyr Babchuk <vlad.babchuk@gmail.com> (RCAR H3/virtualization)
Tested-by Rouven Czerwinski <r.czerwinski@pengutronix.de> (ccimx6ulsbcpro)
Tested-by: Akshay Bhat <akshay.bhat@timesys.com> (Atmel SAM)
Tested-by: Joakim Bech <joakim.bech@linaro.org> (Rpi3b)
Tested-by: Jerome Forissier <jerome.forissier@linaro.org> (QEMU, GP)
Tested-by: Jerome Forissier <jerome.forissier@linaro.org> (QEMUv8, GP)
Tested-by: Victor Chong <victor.chong@linaro.org> (HiKey620 AOSP, HiKey960 AOSP)
Tested-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org> (bpi0)
Tested-by: Igor Opaniuk <igor.opaniuk@gmail.com> (Poplar)
Tested-by: Etienne Carriere <etienne.carriere@linaro.org> (stm32mp1, GP)

CHANGELOG.md

@@ -1,3 +1,13 @@
+# OP-TEE - version 3.6.0 (2019-07-05)
+
+- Link to the GitHub [release page][github_release_3_6_0].
+- Links to the [commits][github_commits_3_6_0] and
+[pull requests][github_pr_3_6_0] merged into this release.
+
+[github_release_3_6_0]: https://github.com/OP-TEE/optee_os/releases/tag/3.6.0
+[github_commits_3_6_0]: https://github.com/OP-TEE/optee_os/compare/3.5.0...3.6.0
+[github_pr_3_6_0]: https://github.com/OP-TEE/optee_os/pulls?q=is%3Apr+is%3Amerged+base%3Amaster+merged%3A2019-04-26..2019-07-05
+
 # OP-TEE - version 3.5.0 (2019-04-26)
 
 - Link to the GitHub [release page][github_release_3_5_0].