add instructions for the web demo #245

Job	Run time
Generate the SWIG wrappers	1m 22s
Lint	20s
Build ASAN instrumented version / Build ASAN on ubuntu-latest	4m 58s
Build code coverage instrumented version / Build codecov on ubuntu-latest	6m 47s
Build native / Build native on macos-latest	5m 8s
Build native / Build native on macos-latest w/o libtiff	4m 9s
Build native / Build native on ubuntu-latest w/o libtiff	5m 1s
Build native / Build native on ubuntu-latest	5m 5s
Build native / Build native on windows-latest w/o libtiff	8m 12s
Build native / Build native on windows-latest	10m 10s
Build WASM / Build wasm on ubuntu-latest w/o libtiff w/o proj.db	8m 4s
Build WASM / Build wasm on ubuntu-latest w/o proj.db	9m 24s
Build WASM / Build wasm on ubuntu-latest w/o libtiff	8m 15s
Build WASM / Build wasm on ubuntu-latest	10m 10s
Run asan	1m 2s
Run code coverage	58s
Test ubuntu-latest	56s
Test ubuntu-latest w/o libtiff	59s
Test ubuntu-latest w/o proj.db	48s
Test ubuntu-latest w/o libtiff w/o proj.db	57s
Test macos-latest	49s
Test macos-latest w/o libtiff	53s
Test macos-latest w/o proj.db	51s
Test macos-latest w/o libtiff w/o proj.db	35s
Test windows-latest	1m 46s
Test windows-latest w/o libtiff	1m 44s
Test windows-latest w/o proj.db	1m 40s
Test windows-latest w/o libtiff w/o proj.db	1m 45s
	1h 42m 48s

Provide feedback