add struct component context consumpion doc

[voidpumpkin]

Description

Fixes #2189

Checklist

• I have run cargo make pr-flow
• I have reviewed my own code
• I have added tests

[github-actions]

Visit the preview URL for this PR (updated for commit 8374d89):

https://yew-rs--pr2533-doccu-context-0k5z4bfg.web.app

_{(expires Sun, 27 Mar 2022 09:38:32 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}

[github-actions]

Size Comparison

examples	master (KB)	pull request (KB)	diff
boids	304.595	304.595	0
contexts	217.709	226.549	+8.840
counter	157.687	157.687	0
dyn_create_destroy_apps	166.176	166.176	0
file_upload	187.256	187.256	0
function_memory_game	344.588	344.588	0
function_router	22.254	22.254	0
function_todomvc	320.395	320.395	0
futures	356.007	356.007	0
game_of_life	199.937	199.937	0
inner_html	149.620	149.620	0
js_callback	165.002	165.002	0
keyed_list	322.361	322.361	0
mount_point	156.794	156.794	0
nested_list	218.416	218.416	0
node_refs	164.282	164.282	0
password_strength	1845.914	1845.914	0
portals	170.833	170.833	0
router	582.700	582.700	0
suspense	215.878	215.878	0
timer	163.490	163.490	0
todomvc	263.836	263.836	0
two_apps	159.090	159.090	0
webgl	163.839	163.839	0