docs: add el7 and wheezy to the list of supported distros
docs: add el7 and wheezy to the list of supported distros

Lucky for me, the existing documentation for RHEL and "Ubuntu or Debian"
didn't need any changes.

Note that I didn't add links to the "Kudu Package Locations" section as any
new links would be broken right now.

Change-Id: I2cfa080f3b3759d4998dead9484fa960ea19f2eb
Reviewed-on: http://gerrit.cloudera.org:8080/1877
Reviewed-by: Jean-Daniel Cryans
Tested-by: Internal Jenkins

helifu/kudu,InspurUSA/kudu,andrwng/kudu,helifu/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,andrwng/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,cloudera/kudu,andrwng/kudu,InspurUSA/kudu,helifu/kudu,EvilMcJerkface/kudu,cloudera/kudu,andrwng/kudu,InspurUSA/kudu,andrwng/kudu,andrwng/kudu,cloudera/kudu,andrwng/kudu,cloudera/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,andrwng/kudu,helifu/kudu,andrwng/kudu,helifu/kudu,EvilMcJerkface/kudu,cloudera/kudu,cloudera/kudu,cloudera/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,cloudera/kudu,EvilMcJerkface/kudu,cloudera/kudu,helifu/kudu,InspurUSA/kudu,EvilMcJerkface/kudu