README.OE-Core.md: fix markdown style issues

Fix markdown style issues using markdownlint tool [1]:

$ cat README.OE-Core.md | mdl
(stdin):15: MD012 Multiple consecutive blank lines
(stdin):9: MD034 Bare URL used
(stdin):13: MD034 Bare URL used
(stdin):19: MD034 Bare URL used
(stdin):25: MD046 Code block style
(stdin):29: MD046 Code block style
(stdin):33: MD046 Code block style

[1] https://github.com/markdownlint/markdownlint
(From OE-Core rev: 64281b59e8bbae75a1706052ff6fba191d86d0d7)

Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

README.OE-Core.md

@@ -6,28 +6,27 @@ of OpenEmbedded. It is distro-less (can build a functional image with
 DISTRO = "nodistro") and contains only emulated machine support.
 
 For information about OpenEmbedded, see the OpenEmbedded website:
-    https://www.openembedded.org/
+<https://www.openembedded.org/>
 
 The Yocto Project has extensive documentation about OE including a reference manual
 which can be found at:
-    https://docs.yoctoproject.org/
-
+<https://docs.yoctoproject.org/>
 
 Contributing
 ------------
 
-Please refer to our contributor guide here: https://docs.yoctoproject.org/dev/contributor-guide/
+Please refer to our contributor guide here: <https://docs.yoctoproject.org/dev/contributor-guide/>
 for full details on how to submit changes.
 
 As a quick guide, patches should be sent to openembedded-core@lists.openembedded.org
 The git command to do that would be:
 
-     git send-email -M -1 --to openembedded-core@lists.openembedded.org
+```
+git send-email -M -1 --to openembedded-core@lists.openembedded.org
+```
 
 Mailing list:
-
-    https://lists.openembedded.org/g/openembedded-core
+<https://lists.openembedded.org/g/openembedded-core>
 
 Source code:
-
-    https://git.openembedded.org/openembedded-core/
+<https://git.openembedded.org/openembedded-core/>