doc: update and add missing docs

src/lib.rs

-//! A wrapper around prometheus_http_query with additional features for ease of use
-//!
-//! All HTTP requests are made using the `reqwest` client
+#![doc = include_str!("../README.md")]
 
 pub mod query;
 
@@ -55,13 +53,18 @@ impl QueryManager {
         self
     }
 
-    /// Set HTTP method to use to send queries to the server
+    /// Set HTTP method to use to send queries to the server (default: `Get`)
     pub fn method(&mut self, method: Method) -> &mut Self {
         self.method = method;
         self
     }
 
     /// Send a query to the Prometheus server and retreived deserialized data
+    ///
+    /// This method accepts any type that implements the `IntoQuery` trait.
+    /// The trait is implemented for `&str`, `String`, `&String`, and __mquery's__
+    /// internal types such as [`query::Metric`], [`query::Scalar`] and others that result
+    /// from the query builder API.
     pub async fn query<Q: IntoQuery>(&self, query: Q) -> Result<PromqlResult, Error> {
         let mut builder = self.client.query(query.into_query().as_ref());
         if let Some((name, val)) = self.auth.get_header() {
@@ -77,6 +80,11 @@ impl QueryManager {
     }
 
     /// Send a ranged query to the Prometheus server and retreived deserialized data
+    ///
+    /// This method accepts any type that implements the `IntoQuery` trait.
+    /// The trait is implemented for `&str`, `String`, `&String`, and __mquery's__
+    /// internal types such as [`query::Metric`], [`query::Scalar`] and others that result
+    /// from the query builder API.
     pub async fn query_range<Q: IntoQuery>(
         &self,
         query: Q,
@@ -101,6 +109,9 @@ impl QueryManager {
 }
 
 // TODO: Add support for basic auth as well
+/// Authentication method
+///
+/// Used in [`QueryManager::auth`] to set the authentication type
 #[derive(Default, Clone, Debug)]
 pub enum Auth {
     #[default]
@@ -125,6 +136,10 @@ impl Auth {
     }
 }
 
+/// HTTP method to use to send queries
+///
+/// This is used by the [`QueryManager::method`] method to set the HTTP
+/// method used to send queries to the server.
 #[derive(Clone, Copy, Debug, Default)]
 pub enum Method {
     #[default]
@@ -132,6 +147,8 @@ pub enum Method {
     Post,
 }
 
+// Private trait used to seal other traits to disallow users from implementing
+// them directly
 pub(crate) mod seal {
     pub(crate) trait Sealed {}
 }

src/query/mod.rs

+//! The query builder API
+//!
+//! [`Metric`] and [`Scalar`] are the basic types used for building queries.
+//! For building complex queries involving operators, see module [`ops`].
+
 use std::fmt::Display;
 
 use crate::seal::Sealed;
@@ -50,6 +55,9 @@ pub struct Metric<'a> {
 
 impl<'a> Metric<'a> {
     /// Create a new metric with a metric name (for example `total_http_requests`)
+    ///
+    /// A metric can be constructed with an empty string as well, however, it's important to
+    /// have at least one label matcher present for the query to be valid.
     pub fn new(name: &'a str) -> Self {
         Self {
             name,