minor doc correction

Author: franckgaga

docs/src/manual/linmpc.md

@@ -21,8 +21,8 @@ outputs are the liquid level ``y_L`` and temperature ``y_T``:
 The following figure depicts the instrumentation installed on the CSTR:
 
 ```@raw html
-<img src="../../assets/cstr.svg" alt="cstr" width=275 style="background-color:white; 
-    border:20px solid white; display: block; margin-left: auto; margin-right: auto;"/>
+<p><img src="../../assets/cstr.svg" alt="cstr" width=275 style="background-color:white; 
+    border:20px solid white; display: block; margin-left: auto; margin-right: auto;"/></p>
 ```
 
 At the steady-state operating points:

docs/src/manual/nonlinmpc.md

@@ -20,8 +20,8 @@ vectors are:
 The following figure presents the system:
 
 ```@raw html
-<img src="../../assets/pendulum.svg" alt="pendulum" width=200 style="background-color:white; 
-    border:20px solid white; display: block; margin-left: auto; margin-right: auto;"/>
+<p><img src="../../assets/pendulum.svg" alt="pendulum" width=200 style="background-color:white; 
+    border:20px solid white; display: block; margin-left: auto; margin-right: auto;"/></p>
 ```
 
 The plant model is nonlinear: