Add mongosh guide doc

doc/mongodb/basic-mongosh.md

+# Basic knowledge for using the MongoDB Shell
+
+The documentation how to use the MongoDB Shell is found here: https://www.mongodb.com/docs/mongodb-shell/run-commands/
+It is recommended to make active use of this documentation.
+
+## Easy step by step guide
+Run and try to understand the following commands:
+```javascript
+use products  // switches to db products (creates one if not existent)
+
+// insert one document
+db.test.insertOne({"name" : "OST"})
+
+// insert many documents
+db.fakestore.insertMany([
+    {
+      "id": 1,
+      "title": "Fjallraven - Foldsack No. 1 Backpack, Fits 15 Laptops",
+      "price": 109.95,
+      "description": "Your perfect pack for everyday use and walks in the forest. Stash your laptop (up to 15 inches) in the padded sleeve, your everyday",
+      "category": "men's clothing",
+      "image": "https://fakestoreapi.com/img/81fPKd-2AYL._AC_SL1500_.jpg",
+      "rating": {
+        "rate": 3.9,
+        "count": 120
+      }
+    },
+    {
+      "id": 2,
+      "title": "Mens Casual Premium Slim Fit T-Shirts ",
+      "price": 22.3,
+      "description": "Slim-fitting style, contrast raglan long sleeve, three-button henley placket, light weight & soft fabric for breathable and comfortable wearing. And Solid stitched shirts with round neck made for durability and a great fit for casual fashion wear and diehard baseball fans. The Henley style round neckline includes a three-button placket.",
+      "category": "men's clothing",
+      "image": "https://fakestoreapi.com/img/71-3HjGNDUL._AC_SY879._SX._UX._SY._UY_.jpg",
+      "rating": {
+        "rate": 4.1,
+        "count": 259
+      }
+    }
+    ])
+
+// find documents with a field "price" with value 22.3
+db.fakestore.find({"price" : 22.3})
+
+// find documents with a field "category" with value "men's clothing" and a field "price" with a value greater than 20.0
+db.fakestore.find({"category":"men's clothing", "price" : {$gt: 20.0}})
+
+// update the price of the "Mens Casual Premium Slim Fit T-Shirts"
+db.fakestore.updateOne( {"title": "Mens Casual Premium Slim Fit T-Shirts "},
+{
+  $set: {
+    "price": 25.5
+  }
+
+// delete all documents that have a field "price" with value 109.95
+db.fakestore.deleteMany({"price" : 109.95})
+
+```
+
+## Notes
+The example data used above belongs to https://fakestoreapi.com/.
+