Add documentation for some entrypoints

Author: aumetra

src/pages/core/entrypoints.mdx

@@ -17,7 +17,7 @@ these entrypoints, each one different from the last.
 In this section we want to give you a quick overview over all the entrypoints
 and when they are called.
 
-## Define entrypoints
+## Defining entrypoints
 
 While you will learn all about entrypoints in the next sections, we want to give
 you an idea on how to define an entrypoint in the first place.
@@ -34,14 +34,22 @@ VM: "Hey! This is an entrypoint, please use it when needed!"
   including the correct function signature.
 </Callout>
 
+<Callout>
+  Even though the sections will show you to use `#[entry_point]`, it is
+  recommended to define your endpoints as `#[cfg_attr(not(feature = "library"),
+  entry_point)]`.
+  <br /> The reason behind that is that it allows you to reuse your contract as a
+  library.
+</Callout>
+
 ```rust
 #[entry_point]
 pub fn instantiate(
     deps: DepsMut,
     env: Env,
     info: MessageInfo,
     msg: InstantiateMsg,
-) -> Result<Response, StdError> {
+) -> StdResult<Response> {
     // Do some logic here
     Ok(Response::default())
 }

src/pages/core/entrypoints/execute.mdx

@@ -8,3 +8,25 @@ import Tags from "@/components/Tags";
 <Tags />
 
 # Execute
+
+Execute pretty much does what it says on the tin: It executes some routine in
+your contract after a remote (either another contract or some client) sent a
+message.  
+What sets it apart from other functions is that the contract has mutable access
+to the underlying storage.  
+This allows you to, for example, increment a counter or add a user to a lottery.
+
+## Definition
+
+```rust filename="contract.rs"
+#[entry_point]
+pub fn execute(
+    deps: DepsMut,
+    env: Env,
+    info: MessageInfo,
+    msg: ExecuteMsg,
+) -> StdResult<Response> {
+  // Increment some counter, register a user, spread liberty for super earth!
+  Ok(Response::new())
+}
+```

src/pages/core/entrypoints/instantiate.mdx

@@ -8,3 +8,25 @@ import Tags from "@/components/Tags";
 <Tags />
 
 # Instantiate
+
+This is one of the most fundamental entrypoints. This entrypoint is called once
+during the contract lifecycle.  
+It essentially is there to initialise the state of your contract (for example,
+initialising a counter in storage, etc.).
+
+You can imagine it as the constructor of your contract.
+
+The most basic definition of this endpoint looks like this:
+
+```rust filename="contract.rs"
+#[entry_point]
+pub fn instantiate(
+    _deps: DepsMut,
+    _env: Env,
+    _info: MessageInfo,
+    _msg: InstantiateMsg,
+) -> StdResult<Response> {
+    // TODO: Initialise storage, send out metrics, do mischief
+    Ok(Response::new())
+}
+```

src/pages/core/entrypoints/query.mdx

@@ -8,3 +8,23 @@ import Tags from "@/components/Tags";
 <Tags />
 
 # Query
+
+In the previous section we talked about the
+[`execute` endpoint](./execute.mdx).  
+The `query` endpoint is actually pretty similar to execute with one key
+difference: The storage is only accessible immutably.
+
+This means you can only _read_ from the storage but not _write_ to it.
+
+## Definition
+
+```rust filename="contract.rs"
+#[entry_point]
+pub fn query(
+    _deps: Deps,
+    _env: Env,
+    _msg: QueryMsg,
+) -> StdResult<QueryResponse> {
+  Ok(QueryResponse::default())
+}
+```