docs: added video explanation of jina concepts

[gitcommitshow]

Our community member Aleksa created a detailed video explanation of jina concepts and it's examples. Added link to that video in getting-started/hello-world section for people to learn more about the demo

[github-actions]

Latency summary

Current PR yields:

• 🐎🐎 index QPS at 1351, delta to last 2 avg.: +9%
• 🐎🐎🐎🐎 query QPS at 59, delta to last 2 avg.: +13%
• 🐎🐎🐎🐎 dam extend QPS at 47436, delta to last 2 avg.: +3%
• 🐎🐎🐎🐎 avg flow time within 1.6523 seconds, delta to last 2 avg.: +17%
• 🐢🐢 import jina within 0.3849 seconds, delta to last 2 avg.: -11%

Breakdown

Version	Index QPS	Query QPS	DAM Extend QPS	Avg Flow Time (s)	Import Time (s)
current	1351	59	47436	1.6523	0.3849
2.1.5	1196	52	46315	1.1462	0.4436
2.1.4	1264	51	45219	1.6659	0.4277

Backed by latency-tracking. Further commits will update this comment.