[DOCS][PYTHON] Update embeddings API docs & Example (#516)

This PR adds an overview of embeddings docs:
- 2 ways to vectorize your data using lancedb - explicit & implicit
- explicit - manually vectorize your data using `wit_embedding` function
- Implicit - automatically vectorize your data as it comes by ingesting
your embedding function details as table metadata
- Multi-modal example w/ disappearing embedding function

docs/test/md_testing.js

@@ -8,6 +8,7 @@ const excludedGlobs = [
   "../src/embedding.md",
   "../src/examples/*.md",
   "../src/guides/tables.md",
+  "../src/embeddings/*.md",
 ];
 
 const nodePrefix = "javascript";