Small fixes in the docs

Author: ikorotkin

docs/classes.md

@@ -6,3 +6,6 @@ has_children: true
 ---
 
 # Classes to define DAE system
+
+This section describes all classes needed to define the DAE system.
+{: .fs-6 .fw-300}

docs/quick-start.md

@@ -51,6 +51,14 @@ Below is a simplified procedure of defining and solving the given DAE system usi
 #include <dae-cpp/solver.hpp>
 ```
 
+Optionally, the `daecpp` namespace can be added to the project:
+
+```cpp
+using namespace daecpp;
+```
+
+Alternatively, use `daecpp::` prefix for all `dae-cpp` types and classes.
+
 ### Step 1. Define the mass matrix of the system
 
 The mass matrix contains only one non-zero element:

docs/solver-options.md

@@ -6,7 +6,7 @@ nav_order: 7
 
 # Solver Options class
 
-The Solver Options class, `daecpp::SolverOptions,` allows the user to redefine and fine-tune the DAE solver options. To do so, the user should create an object of the Solver Options class, update parameters of interest by accessing public variables (see [example](#example) below), and then provide the updated object to the solver function `solve`.
+The Solver Options class, `daecpp::SolverOptions`, allows the user to redefine and fine-tune the DAE solver options. To do so, the user should create an object of the Solver Options class, update parameters of interest by accessing public variables (see [example](#example) below), and then provide the updated object to the solver function `solve`.
 
 The table below contains a complete list of all options accessible via the Solver Options class.