feat: Add new documentation files (QuivrHQ#3351)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

backend/docs/docs/examples/index.md

@@ -0,0 +1 @@
+# Examples

backend/docs/docs/vectorstores/faiss.md

@@ -0,0 +1 @@
+# Faiss

backend/docs/docs/vectorstores/index.md

@@ -0,0 +1,2 @@
+# Vector Stores
+

backend/docs/docs/vectorstores/pgvector.md

@@ -0,0 +1 @@
+# PGVector

backend/docs/docs/workflows/examples/chat.md

@@ -0,0 +1 @@
+# Chat

backend/docs/docs/workflows/examples/rag_with_internet.md

@@ -0,0 +1 @@
+# RAG with Internet

backend/docs/docs/workflows/index.md

@@ -0,0 +1 @@
+# Configuration

backend/docs/mkdocs.yml

@@ -53,10 +53,20 @@ nav:
   - Home: 
     - index.md
     - installation.md
-    - Features:
-      - Parsers:
-        - parsers/index.md
-        - parsers/megaparse.md
-        - parsers/simple.md
+    - Parsers:
+      - parsers/index.md
+      - parsers/megaparse.md
+      - parsers/simple.md
+    - Vector Stores:
+      - vectorstores/index.md
+      - vectorstores/faiss.md
+      - vectorstores/pgvector.md
+    - Workflows:
+      - workflows/index.md
+      - Examples:
+        - workflows/examples/chat.md
+        - workflows/examples/rag_with_internet.md
+    - Examples:
+      - examples/index.md
   - Enterprise: https://docs.quivr.app/