twrpme: Update installation instructions for A only & AB devices

*Updated links to platform-tools
*Moved current AB installation method as old by renaming the include & Added new method introduced in https://github.com/TeamWin/android_bootable_recovery/commit/53796e73334ac9d87d4cb5a355fc8c1d205104f6
*Misc updates

Change-Id: I10c695c9e3faab205ee206dc4e261cbc07bcffc8
diff --git a/_xiaomi/xiaomimia2.markdown b/_xiaomi/xiaomimia2.markdown
index 5bda100..74056b3 100644
--- a/_xiaomi/xiaomimia2.markdown
+++ b/_xiaomi/xiaomimia2.markdown
@@ -21,4 +21,4 @@
 
 {% include twrpinstall.html %}
 
-{% include fastbootabinstall.html %}
+{% include fastbootabinstall_old.html %}