chg: [doc] Moved INSTALL files around to reflect a more acurate support landscape.

chg: [doc] Update README.md to explain some of the folders/files.

INSTALL/README.md

@@ -4,9 +4,22 @@ Currently the following install guides are being tested on a regular basis:
 
 ```
 INSTALL.debian9.txt
-INSTALL.debian_testing.txt
 INSTALL.kali.txt
 INSTALL.ubuntu1804.txt
 ```
 
+A folder of interest might be 'old'. In old you will find previous INSTALL guides.
+
+Files prefixed with 'CONFIG.' are CONFIGuration guides and not full blown INSTALL guides.
+
+UPDATE.txt give you a brief overview on how to update MISP to the latest version, as well as some other core dependencies that can be updated.
+
 Install guides with the 'x' prefix, are marked as Experimental.
+
+The following are tested on a semi-regular basis:
+
+```
+xINSTALL.centos7.txt
+xINSTALL.debian_testing.txt
+xINSTALL.Arch.txt
+```