Update Thread.md

Change image to code snippet to resolve issue #590

Author: Amanda Butler

docs/reference/api/rtos/Thread.md

@@ -10,7 +10,64 @@ The Thread class allows defining, creating and controlling parallel tasks.
 
 [![View code](https://www.mbed.com/embed/?type=library)](http://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/classrtos_1_1_thread.html)
 
-<span class="images">![](https://s3-us-west-2.amazonaws.com/mbed-os-docs-images/thread_priority.png)</span>
+```C
+/// Priority values.
+typedef enum {
+  osPriorityNone          =  0,         ///< No priority (not initialized).
+  osPriorityIdle          =  1,         ///< Reserved for Idle thread.
+  osPriorityLow           =  8,         ///< Priority: low
+  osPriorityLow1          =  8+1,       ///< Priority: low + 1
+  osPriorityLow2          =  8+2,       ///< Priority: low + 2
+  osPriorityLow3          =  8+3,       ///< Priority: low + 3
+  osPriorityLow4          =  8+4,       ///< Priority: low + 4
+  osPriorityLow5          =  8+5,       ///< Priority: low + 5
+  osPriorityLow6          =  8+6,       ///< Priority: low + 6
+  osPriorityLow7          =  8+7,       ///< Priority: low + 7
+  osPriorityBelowNormal   = 16,         ///< Priority: below normal
+  osPriorityBelowNormal1  = 16+1,       ///< Priority: below normal + 1
+  osPriorityBelowNormal2  = 16+2,       ///< Priority: below normal + 2
+  osPriorityBelowNormal3  = 16+3,       ///< Priority: below normal + 3
+  osPriorityBelowNormal4  = 16+4,       ///< Priority: below normal + 4
+  osPriorityBelowNormal5  = 16+5,       ///< Priority: below normal + 5
+  osPriorityBelowNormal6  = 16+6,       ///< Priority: below normal + 6
+  osPriorityBelowNormal7  = 16+7,       ///< Priority: below normal + 7
+  osPriorityNormal        = 24,         ///< Priority: normal
+  osPriorityNormal1       = 24+1,       ///< Priority: normal + 1
+  osPriorityNormal2       = 24+2,       ///< Priority: normal + 2
+  osPriorityNormal3       = 24+3,       ///< Priority: normal + 3
+  osPriorityNormal4       = 24+4,       ///< Priority: normal + 4
+  osPriorityNormal5       = 24+5,       ///< Priority: normal + 5
+  osPriorityNormal6       = 24+6,       ///< Priority: normal + 6
+  osPriorityNormal7       = 24+7,       ///< Priority: normal + 7
+  osPriorityAboveNormal   = 32,         ///< Priority: above normal
+  osPriorityAboveNormal1  = 32+1,       ///< Priority: above normal + 1
+  osPriorityAboveNormal2  = 32+2,       ///< Priority: above normal + 2
+  osPriorityAboveNormal3  = 32+3,       ///< Priority: above normal + 3
+  osPriorityAboveNormal4  = 32+4,       ///< Priority: above normal + 4
+  osPriorityAboveNormal5  = 32+5,       ///< Priority: above normal + 5
+  osPriorityAboveNormal6  = 32+6,       ///< Priority: above normal + 6
+  osPriorityAboveNormal7  = 32+7,       ///< Priority: above normal + 7
+  osPriorityHigh          = 40,         ///< Priority: high
+  osPriorityHigh1         = 40+1,       ///< Priority: high + 1
+  osPriorityHigh2         = 40+2,       ///< Priority: high + 2
+  osPriorityHigh3         = 40+3,       ///< Priority: high + 3
+  osPriorityHigh4         = 40+4,       ///< Priority: high + 4
+  osPriorityHigh5         = 40+5,       ///< Priority: high + 5
+  osPriorityHigh6         = 40+6,       ///< Priority: high + 6
+  osPriorityHigh7         = 40+7,       ///< Priority: high + 7
+  osPriorityRealtime      = 48,         ///< Priority: realtime
+  osPriorityRealtime1     = 48+1,       ///< Priority: realtime + 1
+  osPriorityRealtime2     = 48+2,       ///< Priority: realtime + 2
+  osPriorityRealtime3     = 48+3,       ///< Priority: realtime + 3
+  osPriorityRealtime4     = 48+4,       ///< Priority: realtime + 4
+  osPriorityRealtime5     = 48+5,       ///< Priority: realtime + 5
+  osPriorityRealtime6     = 48+6,       ///< Priority: realtime + 6
+  osPriorityRealtime7     = 48+7,       ///< Priority: realtime + 7
+  osPriorityISR           = 56,         ///< Reserved for ISR deferred thread.
+  osPriorityError         = -1,         ///< System cannot determine priority or illegal priority.
+  osPriorityReserved      = 0x7FFFFFFF  ///< Prevents enum down-size compiler optimization.
+} osPriority_t;
+``` 
 
 ### Thread example