[master] Add section on external charts (#5975)
[master] Add section on external charts (#5975)

* Add section on external charts

* Update content/en/docs/setup/install/istioctl/index.md

Co-Authored-By: Frank Budinsky <eff2b2321921dd21161b5817c477702c05bb637b@ca.ibm.com>

* Update content/en/docs/setup/install/istioctl/index.md

Co-Authored-By: Frank Budinsky <eff2b2321921dd21161b5817c477702c05bb637b@ca.ibm.com>

* Update content/en/docs/setup/install/istioctl/index.md

Co-Authored-By: Frank Budinsky <eff2b2321921dd21161b5817c477702c05bb637b@ca.ibm.com>

* Update content/en/docs/setup/install/istioctl/index.md

Co-Authored-By: Frank Budinsky <eff2b2321921dd21161b5817c477702c05bb637b@ca.ibm.com>

* Update content/en/docs/setup/install/istioctl/index.md

Co-Authored-By: Frank Budinsky <eff2b2321921dd21161b5817c477702c05bb637b@ca.ibm.com>

* Spelling

* Update content/en/docs/setup/install/istioctl/index.md

Co-Authored-By: Frank Budinsky <eff2b2321921dd21161b5817c477702c05bb637b@ca.ibm.com>

* Update content/en/docs/setup/install/istioctl/index.md

Co-Authored-By: John Howard <howardjohn@google.com>

* Update content/en/docs/setup/install/istioctl/index.md

Co-Authored-By: Frank Budinsky <eff2b2321921dd21161b5817c477702c05bb637b@ca.ibm.com>

istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io